diff --git a/ZB.MOM.WW.Theme/README.md b/ZB.MOM.WW.Theme/README.md
index a5747ba..0508442 100644
--- a/ZB.MOM.WW.Theme/README.md
+++ b/ZB.MOM.WW.Theme/README.md
@@ -84,8 +84,14 @@ Served at `_content/ZB.MOM.WW.Theme/…` by the ASP.NET static-web-asset pipelin
 
 **Bootstrap button sizing (new in 0.4.0).** The kit now normalizes `.btn` / `.btn-sm` against its
 0.9rem body via `--bs-btn-*` variable overrides, because Bootstrap hard-codes
-`--bs-btn-font-size: 1rem`. All five consuming apps had written this same block into their own
-stylesheets; **delete the local copy when you bump to 0.4.0** (each carries a comment saying so).
+`--bs-btn-font-size: 1rem`. Several consuming apps had written this same block into their own
+stylesheets; **trim the local copy when you bump to 0.4.0** — trim rather than delete, because a
+local `.btn` may also carry app-specific *shape* declarations the kit does not ship.
+
+**This is not universal — check before assuming your app already had it.** HistorianGateway has no
+local `.btn` sizing at all, so for it the bump to 0.4.0+ is a **visible change** (buttons shrink from
+Bootstrap's 1rem to `.85rem`) rather than a no-op cleanup. An earlier version of this note claimed
+all five consumers carried the block; that was wrong.
 Size buttons by overriding the `--bs-btn-*` variables, never by redeclaring box properties — the
 `.btn-group` seam and radius machinery reads those variables, so a literal `font-size` at equal
 specificity silently reduces `.btn-sm` to a padding-only difference.
diff --git a/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css b/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
index 2ab20e6..fa73851 100644
--- a/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
+++ b/ZB.MOM.WW.Theme/src/ZB.MOM.WW.Theme/wwwroot/css/layout.css
@@ -3,10 +3,17 @@
 
 /* ── Bootstrap button sizing ─────────────────────────────────────────────────
    Bootstrap hard-codes --bs-btn-font-size: 1rem, which is oversized against
-   this kit's 0.9rem body. Every consuming app had independently written this
-   same block into its own stylesheet (ignitionoee app.css, OtOpcUa site.css,
-   mxgw site.css, HistorianGateway site.css, ScadaBridge site.css) — it is
-   upstreamed here in 0.4.0, and those local copies can be deleted on bump.
+   this kit's 0.9rem body. Several consuming apps had independently written this
+   same block into their own stylesheets — verified in ignitionoee app.css,
+   OtOpcUa site.css, mxgw site.css and ScadaBridge — so it is upstreamed here in
+   0.4.0 and those local copies can be trimmed on bump.
+
+   NOT universal, despite an earlier claim in this comment that listed all five:
+   HistorianGateway has NO local .btn sizing in either its committed tree or its
+   sweep branch — only vendored bootstrap.min.css. So on 0.3.1 its buttons render
+   at Bootstrap's default 1rem, and its bump to 0.4.0+ is a VISIBLE change (buttons
+   shrink to .85rem), not the no-op cleanup it is for the others. Do not assume a
+   consumer already has this sizing; check before calling a bump cosmetic.
 
    Sized by CSS-variable override ONLY — never by redeclaring box properties.
    Bootstrap's .btn-group seam and radius machinery reads these same variables,