diff --git a/frontend/src/components/Runs/RunsScreen.tsx b/frontend/src/components/Runs/RunsScreen.tsx
index 33cf1aa..cdd4c95 100644
--- a/frontend/src/components/Runs/RunsScreen.tsx
+++ b/frontend/src/components/Runs/RunsScreen.tsx
@@ -723,7 +723,7 @@ function ParamDiff({ rows }: { rows: RunRow[] }) {
   // declaration lookup per flow, and a sweep comparison never does.
   const one = rows.every((run) => run.flow === rows[0].flow)
   const { declared } = useFlowInputs(one ? rows[0].flow : undefined)
-  const varying = varyingKeys(rows)
+  const varying = varyingKeys(rows, declared)
   const keys = new Set<string>()
   for (const run of rows)
     for (const key of Object.keys(run.params)) keys.add(key)
diff --git a/frontend/src/components/Runs/queries.ts b/frontend/src/components/Runs/queries.ts
index d679ba4..ac68873 100644
--- a/frontend/src/components/Runs/queries.ts
+++ b/frontend/src/components/Runs/queries.ts
@@ -310,14 +310,24 @@ export const shortCommit = (commit: string) => commit.slice(0, 7)
  * What makes a sweep readable: fifty runs of one flow share everything but the
  * two knobs that were swept, and those two are the only columns worth drawing.
  */
-export function varyingKeys(runs: { params: Record<string, unknown> }[]) {
+export function varyingKeys(
+  runs: { params: Record<string, unknown> }[],
+  declared: Map<string, unknown> = new Map(),
+) {
   if (runs.length < 2) return []
   const keys = new Set<string>()
   for (const run of runs)
     for (const key of Object.keys(run.params)) keys.add(key)
+  // A key a run lacks is one it took from its flow, read as what the flow
+  // declares now — the value its cell shows.
+  // ponytail: a run from before 2026-08-29 stored only what was passed, so if
+  // its flow's `initial` changed since, a real difference reads as none. Exact
+  // needs the definition at the run's version, which no route serves.
+  const value = (run: (typeof runs)[number], key: string) =>
+    JSON.stringify(key in run.params ? run.params[key] : declared.get(key))
   return [...keys].filter((key) => {
-    const first = JSON.stringify(runs[0].params[key])
-    return runs.some((run) => JSON.stringify(run.params[key]) !== first)
+    const first = value(runs[0], key)
+    return runs.some((run) => value(run, key) !== first)
   })
 }