That’s scary, mum.
Yes; after an extended period of time the plastic wrapping around tampons will gradually allow moisture in, introducing bacteria that will grow very well in that environment. Later, if these tampons are used, they can cause toxic shock syndrome, which can sometimes be fatal.
The use-by date is usually several years away, and they’re probably safe for a while beyond that date too, but it’s not something you want to fuck around with. Still true that “leaving them in too long” is more-likely to be dangerous, but still worth looking at. Check those use-bys, chickadees!