I'm tweaking an old mod, and in order to fix a minor bug, I need a way to detect when the player has loaded a saved game. I know of two ways to do that, but unfortunately one uses SetJournalIndex and one uses a start script—both of which require one of the expansions. I realize that matters to essentially nobody, but just for the sake of keeping mod's requirements the same as when I wrote it, does anybody know another way?

MWSE might be able to do such things, but I believe that requires at least Tribunal, so that might not be any help.
Fliggerty would probably be the best able to answer you.

when in doubt...
Summon: Fliggerty !

Hmm, it looks like the answer was in MSFD all along. Apparently the "ForceSneak" state of actors is not saved, and this can be checked with GetForceSneak. That's actually simpler than some of the other methods too.