So it makes sense to copy branch keys from vc-dir-mode-map
to vc-prefix-map:
diff --git a/lisp/vc/vc-hooks.el b/lisp/vc/vc-hooks.el
index 4b3c829a2c..d039c400c5 100644
--- a/lisp/vc/vc-hooks.el
+++ b/lisp/vc/vc-hooks.el
@@ -865,6 +865,9 @@ vc-prefix-map
(let ((map (make-sparse-keymap)))
(define-key map "a" #'vc-update-change-log)
(define-key map "b" #'vc-switch-backend)
+ (define-key map "Bc" #'vc-create-tag)
+ (define-key map "Bl" #'vc-print-branch-log)
+ (define-key map "Bs" #'vc-retrieve-tag)
(define-key map "d" #'vc-dir)
(define-key map "g" #'vc-annotate)
(define-key map "G" #'vc-ignore)