I feel like you can see the difference from casino to casino if playing the same game. I'll notice a bonus hits more often on xxx site vs another. I could be complately fucked in the head and just be seeing what I want to see, but i'm pretty sure casinos can request different rtps.
That's the fact, providers are been making available different RTP versions for the casinos for many many games.. sometimes with huge difference between the highest and the lowest versions! Most of time you can verify thi in the game on the game informations, but for some providers there is option to not show the RTP!
I think there is been some game that have no different RTP versions, like: ("Sweet Bonanza" Pragmatic and "Guns n Roses" from NETENT.)
My guess is while for the first is question of reputation regarding to the popularity of the game, for the second is maybe due to some clauses of the contract made with the (Guns n Roses) band !!
Sometimes while using the search you can see a casino holding both versions of a same game:
Searching for a game, and guess what !?
I literally found two versions of it, maybe could think that is just a displaying bug, but:
After looking on games infos of each version it is been confirmed
Here the lowered version is called "DX1" !