The main problem with the testing done is that it's all probability maths.
You could collate all the spins from all the active players in a month, and the results would still be only the probability of getting a certain rarity in a certain slot.
It would not reflect if you have that probability because of pre-choice math or post-choice math.

The only way with this would be to crack open the code of the app and check it.

If I had any experience with flash programming I'd do that myself, just to satisfy my curiosity.