I honestly thought, people would keep ownership over the files they bought.
And that is why I rant over this feature. It is misleadingly named. A customer does in fact not buy the files individually. It should be called tiered bonus items or whatever.
It is an attempt of a dlc mechanic, without need for creating separate projects. Ok. But then they should have the functionality, to increase your tier. The feature is broken and unusable except for the most trivial use case: one payment and never changing prices and the user knows at first purchase, which bonus item tier is wanted - and there are projects with several tiers.