Plex sees old TV episodes as new when new shows are added

[OttoKerner]

Recently Added is not accurate

Settings - Server - Library - “Empty trash automatically after every scan” You want to keep that off if there is any chance that access to the media storage can sometimes have waiting times. Like for instance because the hard drive first needs to spin up its platters from idle state. Or because sometimes the network file share will not react promptly.

There is also a slight chance of mismatches if you keep adding more and more media – if you started out with not adhering to the best practices regarding folder organization and file naming.
https://support.plex.tv/articles/categories/your-media/