They post older and newer stuff both on the timeline and inbox, you just gotta be able to tell whats "new" based on her looks if that makes sense. If I were you I'd get more familiar with what is on the content sub bc a lot of what you've posted is already there. I wouldn't say they sell old stuff to newer subs, that wouldn't make any sense to attempt to do anyways bc that requires keeping track of who buys what and nobody can really do that efficiently, even with an agency running who has multiple people at the desk. It's an organizational nightmare.
For me, I'm fairly familiar with what she looks like over time, her activities content-wise, the outfits etc. Plus like Ive said before Ive combed through the content thread multiple times. Yes, its super meticulous but I always try to make sure whatever I post is new, or at least unseen and I have on a few occasion deleted or removed items if I later find its a repost. I dont expect everyone to be like that but I do wish people would make more of an effort to not run to post in the thread just bc something popped up on her timeline or DMs...or found elsewhere.