In CAS ( shift + click on sim cheat ), at first everything seems fine with the sim... until switching view to a different outfit. Switching to formal changes the hair. Switching back to everyday changes the hair to something different than it was before! It's like a TS3 hair troll is messing with me. This started happening sometime after installing 70s 80s and 90s Stuff. Is my game getting corrupt?

Edit:
It's only happening to this one sim. The other sims in the household aren't affected.

If it wasn't switching to a different everyday hairstyle when you switch back to the everyday outfit I would wonder if somehow the hairstyle toggle got unlocked to set different hairstyles for each outfit.

I'm still wondering if turning that toggle off and on a few times might help.

Thanks, I tried and the lock will apply to any other hair. Something I noticed: Once the original hair is gone there's no way to get it back. Is it possible that sims can wear a temp copy of hair that shows on the sim even after the mod is removed? Can't find that hair at all in the hair library.
I think this is solved now, because I vaguely remember that it is from a foreign site. Thanks again for making it easier to see what's wrong.

If you haven't cleared your caches, then yes. the old hairstyle is probably still cached. (DO NOT DELETE the DCCache. Despite having "Cache" in its name it's not one that you want to clear. It's your installed Sims 3 Packs.)

Some CC also comes attached to a sim and doesn't show up anywhere else, although you can usually solve that by removing it from the sim who is using it and making sure the DCBackup doesn't have it (which is a difficult task since the DCBackup gives everything a name that looks as though someone spilled a bowl of alphabet soup.)

But since the game is having trouble putting that hairstyle onto a sim, it's probably one that will be gone as soon as you clear your caches.