No longer current, while still appearing so. Staleness is dangerous exactly because it looks like freshness.
Anglo-French estaler (to stand still, to cease flowing), originally used of ale or wine that had stopped fermenting and gone flat; a thing gone stale still looks the same while everything active in it has stopped.
No longer current, while still wearing the appearance of being so. The danger is old: the word first named flat ale that still looked like a drink.