As for the RTP of those slots where you can win an unlimited amount of free spins(I actually think it's limited at a certain number), I think all those wins will be taken into account when regulators/auditors carry out verification of whether the stated RTP is equal to the real one.
If there is no a maximum theorical cap for winnings hit, it can affect negatively the (medium returns), or those average or medium wins that allows you to play and wager higher amount than your bance..
The fact that an unlimited win can really occur mean also that you can place unlimited amounts without any win..
Let me give you an example.. For the game "Sweet Bonanza" for example, as they say:
Additionally to that, during the bonus rounds hitting 3 or more lollipops give you an extra 5 free spins.. so it can continue indefinitely
so each and both the facts points to that there is no a maximum possible win !
For the calculation, if we take for example a random number generator, and consider just the one digit number on the right.. then the probability to get each digit at this position is 1 per 10.... then the probability calculus is here, but there is still chance, or possibility to get one or ever more digits never drawn at this position.. !
I tried to recover the thread.. but it is dated from about three years of now, I will give it another try..
He have get that on some game related to (Olympus gods), and I think that could maybe was a Pragmatic game as he posted a reply of his win. he was playing at $3 single bet ( or $30 ), and he get constant bonuses activated during the bonus round.. this like till hitting a very huge amount.
I remember at the end, LoyceV asked him how he accepted to renounce and accept the small "consolation" amount they give him, but he didn't respond.
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