Thank you all for your comments. I haven’t been able to respons due to RL, but here goes.
Disclaimer - I do not accuse anyone of wrong doing, since I have no proof of that. If you think that I‘m to critical, then that was not my intention. All I would like is a clarification to remove the sour feelings I have due to poor luck.
I asked my original question, since I wanted to know where to look for the “law” since Apple did not have a page (That I could find). @Laeuftbeidir thank you for stating what I should have know. There is only a useless rule from Apple, which is not enforced, so any developer in the App-store can write whatever drop rate they want. Should they get “caught” by Apple they have 30 days to fix the “error”.
How any developer is supposed to be caugth by Apple, if Apple do not collect any documentation is anyone’s guess. I suppose we have to hope for a disgruntled worker.
@nerdstrap - I know there is something called selection bias, that is why I asked for documentation. By looking at data for all drops I could see if the specification was valid, e.g. that the actual drop rates are consistent with what several of you have pointed me towards - the %-part of the vault.
Here is my problem with the % in the vault. If that was documentation, then I would assume there would be some kind of fluctuation in these numbers, since if truly random there would be bad/good streaks. However, once set the rates seem to remind fixed. So the % is not documentation of a correctly working functionality. It describes the “goal” or expected behaviour.
Let us assume that software developers can make mistakes! I know that is a bit far fetched but humor me please. For my part I think that it is entirely possible that Octagon could make a mistake during coding. If you have played MTGPQ, I think you know what I mean.
Now is Octagon changing code that relates to the drop rate?
Well I would like to turn your attention to the release of Ixalan, where we got abysmal drop rates, at something between 2-3 % Those drop rates was changed once most of the hoarded crystals was spent (or Apple had made D3/Octagon aware of the mistake).
Recently Brigby confirmed that an error had occurred in the Pink+ pack, so one Masterpiece was not lootable!
So my assumption that Octagon is altering in the packs and the drop rates from time to time Is not invalid.
@brigby has stated around the time Ixalan was released that the drop rates in some way is related the number of cards there is in each rarity. But this seems to be a misconstrued perception, when the drop rates for Ixalan is definitely different now as opposed to release.
So I ask D3/Octagon - How do you test/validate the drop rates internally?
How do you arrive at the drop rates in the UI?
I assume that you must have some sort of data collection performed to prove to Apple that your drop rates in the %-part of the vault are reseasonably correct.
How often is that report generated?
Who recieves this report in D3/Octagon and outside of these firms?
What is you policy for correcting errors and compensating users if/when errors are found?
Post script - Sorry this became such a long response, but I got inspired. 
Post Post script - @Volrak - I think that your work for the community is recommendable, thank you for your hard work and thank you to all who helped collect the data. I have never participated, because I think that your results should be coming from Octagon not you. 