diff --git a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
index b3aabfa..79b4345 100644
--- a/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
+++ b/modules/mesh-delivery-checker/cmd/mesh-delivery-checker/forge.go
@@ -20,6 +20,8 @@ const (
 	getFileTool = "gitea.gitea_get_file"
 	compareTool = "gitea.gitea_compare"
 	commitsTool = "gitea.gitea_commits"
+	// gitea_list_branches answers {branches: [{name, commit}]}, every branch with the commit it points at.
+	branchesTool = "gitea.gitea_list_branches"
 )
 
 // notFoundStatus is the 404 of the forge's error, `Gitea API <path>: <status> <body>`.
@@ -102,3 +104,26 @@ func (f forgeReads) FullSHA(_ context.Context, repository, commit string) (strin
 	}
 	return a.Commits[0].SHA, nil
 }
+
+// BranchHeads is the commit each branch of the repository points at.
+func (f forgeReads) BranchHeads(_ context.Context, repository string) (map[string]string, error) {
+	owner, repo := ownerRepo(repository)
+	raw, err := f.ask(branchesTool, map[string]string{"owner": owner, "repo": repo})
+	if err != nil {
+		return nil, err
+	}
+	var a struct {
+		Branches *[]struct {
+			Name   string `json:"name"`
+			Commit string `json:"commit"`
+		} `json:"branches"`
+	}
+	if err := json.Unmarshal(raw, &a); err != nil || a.Branches == nil {
+		return nil, fmt.Errorf("the answer of %s is not {branches: [{name, commit}]}: %v", branchesTool, err)
+	}
+	heads := map[string]string{}
+	for _, b := range *a.Branches {
+		heads[b.Name] = b.Commit
+	}
+	return heads, nil
+}
diff --git a/modules/mesh-delivery-checker/internal/check/case.go b/modules/mesh-delivery-checker/internal/check/case.go
index 22850d4..1c99029 100644
--- a/modules/mesh-delivery-checker/internal/check/case.go
+++ b/modules/mesh-delivery-checker/internal/check/case.go
@@ -3,6 +3,7 @@ package check
 import (
 	"fmt"
 	"maps"
+	"slices"
 	"sort"
 	"strings"
 	"sync"
@@ -40,6 +41,9 @@ type Case struct {
 	Queued time.Time
 	// Try narrows a try's check (its level, its tests); nil for a pull request's.
 	Try *TryOptions
+
+	notesMu sync.Mutex
+	notes   []string
 	// Progress says what the check is doing, so a check that ran past its bound names the step it was stuck at.
 	Progress *Progress
 	// Kind is what asked the check (KindNew, KindNodes, KindTrunk): a re-judge after a trunk move is asked on the build
@@ -148,3 +152,19 @@ func (t *Trunks) Heads() map[string]string {
 	defer t.mu.Unlock()
 	return maps.Clone(t.heads)
 }
+
+// note puts a word of the check's way on the case, for a try's line (issue 1921).
+func (c *Case) note(s string) {
+	c.notesMu.Lock()
+	defer c.notesMu.Unlock()
+	if !slices.Contains(c.notes, s) {
+		c.notes = append(c.notes, s)
+	}
+}
+
+// Notes are the words noted on the case, in the order they were noted.
+func (c *Case) Notes() []string {
+	c.notesMu.Lock()
+	defer c.notesMu.Unlock()
+	return slices.Clone(c.notes)
+}
diff --git a/modules/mesh-delivery-checker/internal/check/pins.go b/modules/mesh-delivery-checker/internal/check/pins.go
index c07a8c4..1de0a6e 100644
--- a/modules/mesh-delivery-checker/internal/check/pins.go
+++ b/modules/mesh-delivery-checker/internal/check/pins.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"path"
 	"regexp"
+	"sort"
 	"strings"
 )
 
@@ -36,6 +37,8 @@ type Forge interface {
 	OnTrunk(ctx context.Context, repository, commit string) (bool, error)
 	// FullSHA is the 40-digit sha of a commit named by its first 12 digits.
 	FullSHA(ctx context.Context, repository, commit string) (string, error)
+	// BranchHeads is the commit every branch of a repository points at, by branch name (issue 1921).
+	BranchHeads(ctx context.Context, repository string) (map[string]string, error)
 }
 
 var pseudoVersion = regexp.MustCompile(`-([0-9a-f]{12})$`)
@@ -93,6 +96,18 @@ func (st *state) checkPinsOf(ctx context.Context, t *target) verdictPtr {
 			if onTrunk {
 				continue
 			}
+			if st.c.Try != nil {
+				// A try only (issue 1921): a repository tried on a branch that mesh-sdk shares by name (a milestone's branch across
+				// repositories) is built with that branch's mesh-sdk head, which no group pull request holds before the pull requests exist.
+				branch, err := st.sameBranchPin(ctx, t, pin)
+				if err != nil {
+					return failed(forgeMachine(err, t.node), fmt.Sprintf("%s#%d: whether mesh-sdk %s is the head of a branch cannot be told: %v%s", t.pull.Repository, t.pull.Number, pin, err, unheardWords(err)))
+				}
+				if branch != "" {
+					st.c.note(fmt.Sprintf("pin accepted: head of mesh-sdk %s", branch))
+					continue
+				}
+			}
 			nor := "the group has no mesh-sdk pull request"
 			if sdk != nil {
 				nor = "the head of the group's mesh-sdk pull request is " + short12(sdk.Head)
@@ -103,6 +118,35 @@ func (st *state) checkPinsOf(ctx context.Context, t *target) verdictPtr {
 	return nil
 }
 
+// sameBranchPin names the branch of the tried repository that points at the tried head and that mesh-sdk also has, at the
+// commit the pin names; empty when there is none.
+func (st *state) sameBranchPin(ctx context.Context, t *target, pin string) (string, error) {
+	mine, err := st.j.Forge.BranchHeads(ctx, t.pull.Repository)
+	if err != nil {
+		return "", err
+	}
+	var same []string
+	for name, head := range mine {
+		if head == t.pull.Head && name != "main" {
+			same = append(same, name)
+		}
+	}
+	if len(same) == 0 {
+		return "", nil
+	}
+	sdk, err := st.j.Forge.BranchHeads(ctx, SDKRepository)
+	if err != nil {
+		return "", err
+	}
+	sort.Strings(same)
+	for _, name := range same {
+		if h, ok := sdk[name]; ok && strings.HasPrefix(h, pin) {
+			return name, nil
+		}
+	}
+	return "", nil
+}
+
 // failureVerdict is a verdict of failure the check ends with.
 
 // pinHint is added to the failure of a Go member's fetch that names mesh-sdk while the group holds a mesh-sdk pull request:
diff --git a/modules/mesh-delivery-checker/internal/check/pins_test.go b/modules/mesh-delivery-checker/internal/check/pins_test.go
index d1083be..0c4dba0 100644
--- a/modules/mesh-delivery-checker/internal/check/pins_test.go
+++ b/modules/mesh-delivery-checker/internal/check/pins_test.go
@@ -18,6 +18,15 @@ type fakeForge struct {
 	onTrunk map[string]bool   // by commit prefix
 	err     error
 	errAt   map[string]error // by ref: a read at that ref fails with it
+	// branches are the branches of a repository with the commit each points at.
+	branches map[string]map[string]string
+}
+
+func (f *fakeForge) BranchHeads(_ context.Context, repository string) (map[string]string, error) {
+	if f.err != nil {
+		return nil, f.err
+	}
+	return f.branches[repository], nil
 }
 
 func (f *fakeForge) File(_ context.Context, repository, path, ref string) (string, error) {
@@ -358,3 +367,44 @@ func TestTheNodeEnginesCheckFailsWhereTheControllersTrunkIsNotKnown(t *testing.T
 		t.Fatalf("verdict = %+v", v)
 	}
 }
+
+// sameBranchBench is a try of mesh-delivery's feat/r6 at head1 whose go.mod pins the SDK at pin, with the SDK's feat/r6 at head2.
+func sameBranchBench(t *testing.T, pin string) (*bench, *Case) {
+	b := groupBench(t, pin)
+	b.ex.Forge.(*fakeForge).branches = map[string]map[string]string{
+		repoA:   {"main": trunkA, "feat/r6": head1},
+		repoSDK: {"main": "cb54756c3865" + strings.Repeat("0", 28), "feat/r6": head2},
+	}
+	c := caseOf(t, pullOf(repoA, 7, head1))
+	c.Try = &TryOptions{}
+	return b, c
+}
+
+func TestATryPinnedToTheHeadOfTheSDKBranchOfTheTriedBranchPasses(t *testing.T) { // 1921/AC1
+	b, c := sameBranchBench(t, head2[:12])
+	if v := b.judge(t, c).Verdict; v.State != delivery.VerdictPass {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if n := c.Notes(); len(n) != 1 || n[0] != "pin accepted: head of mesh-sdk feat/r6" {
+		t.Errorf("notes = %q", n)
+	}
+}
+
+func TestATryPinnedToAnotherCommitIsStillRefused(t *testing.T) { // 1921/AC2
+	b, c := sameBranchBench(t, "9aaa5c80ac5c")
+	v := b.judge(t, c).Verdict
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "9aaa5c80ac5c") || !strings.Contains(v.Failed.Words, "neither on mesh-sdk's trunk nor the group's head") {
+		t.Fatalf("verdict = %+v", v)
+	}
+	if len(c.Notes()) != 0 {
+		t.Errorf("notes = %q", c.Notes())
+	}
+}
+
+func TestAMergeCheckWithTheSameBranchPinIsStillRefusedWithoutAGroupPullRequest(t *testing.T) { // 1921/AC3
+	b, _ := sameBranchBench(t, head2[:12])
+	v := b.judge(t, caseOf(t, pullOf(repoA, 7, head1))).Verdict // no Try: a pull request's check
+	if v.State != delivery.VerdictFail || !strings.Contains(v.Failed.Words, "the group has no mesh-sdk pull request") {
+		t.Fatalf("verdict = %+v", v)
+	}
+}
diff --git a/modules/mesh-delivery-checker/internal/check/try.go b/modules/mesh-delivery-checker/internal/check/try.go
index 812773b..5f0be8b 100644
--- a/modules/mesh-delivery-checker/internal/check/try.go
+++ b/modules/mesh-delivery-checker/internal/check/try.go
@@ -329,6 +329,9 @@ func (tr *Tryer) run(ctx context.Context, key string) {
 	t.Took = t.Ended.Sub(t.Started).Round(time.Second).String()
 	t.Levels, t.Machines = v.Levels, v.Machines
 	t.Said = Report(v, cs, cs.Pulls[0], out.Builds, out.Slowest, out.Judged)
+	for _, n := range cs.Notes() {
+		t.Said += " | " + n
+	}
 	switch {
 	case !judged || IsNodesFailure(v):
 		t.State = TryError
diff --git a/modules/mesh-delivery-checker/manifest_test.go b/modules/mesh-delivery-checker/manifest_test.go
index c6af543..8df57af 100644
--- a/modules/mesh-delivery-checker/manifest_test.go
+++ b/modules/mesh-delivery-checker/manifest_test.go
@@ -103,7 +103,7 @@ func TestManifestDeclarations(t *testing.T) { // 1678/AC1
 	}
 	// 1887/A5b: the checker reads nothing of the controller's plans-building (ADR 0483 superseded by ADR 0525 §7), calls no
 	// build module's tool and holds no capacity: it puts check asks on the Go and Node build seats (ADR 0525 §1, §4).
-	if want := []string{"gitea.gitea_commits", "gitea.gitea_compare", "gitea.gitea_get_file"}; !reflect.DeepEqual(sorted(m.Invokes), want) {
+	if want := []string{"gitea.gitea_commits", "gitea.gitea_compare", "gitea.gitea_get_file", "gitea.gitea_list_branches"}; !reflect.DeepEqual(sorted(m.Invokes), want) {
 		t.Errorf("invokes = %v, want only the forge's reads for a mesh-sdk pin (ADR 0484 clause 9)", m.Invokes)
 	}
 	if want := []string{"node-build-go", "node-build-node"}; !reflect.DeepEqual(sorted(m.Uses), want) {
diff --git a/modules/mesh-delivery-checker/module.json b/modules/mesh-delivery-checker/module.json
index 67c97f2..c53c7b5 100644
--- a/modules/mesh-delivery-checker/module.json
+++ b/modules/mesh-delivery-checker/module.json
@@ -47,7 +47,8 @@
   "invokes": [
     "gitea.gitea_commits",
     "gitea.gitea_compare",
-    "gitea.gitea_get_file"
+    "gitea.gitea_get_file",
+    "gitea.gitea_list_branches"
   ],
 
   "own-secrets": {