I believe they might have changed their tactics regarding this, at least on Renderotica.
I recently checked something I bought a few weeks back and YES there was a license PDF but nothing was particularly notable about it, except the MODIFIED date which was set exactly 5 hours before my DOWNLOADED time. Actually all files had this same modified time, which had nothing to do with any upload or update by the creator.
This might mean that they are now actually tracking by their SERVER TIME and not by your local time, and simply modifying files to mark the time it was bought/downloaded is a way sneakier and more annoying tactic as it forces you to modify all files yourself just to counter that if you want to upload here.
Yes, what @medusa said 🙂