I'd define it as 'everything you've documented so far still works as documented, and possibly if you're aware that many of your downstreams are relying on some

I'd define it as 'everything you've documented so far still works as documented, and possibly if you're aware that many of your downstreams are relying on some undocumented behaviour, you try to account for that too (but that part is a nicety, not a commitment).