As far as I know, before a physical slot machine will be used in actual live gambling, there are checking and auditing on how that machine works, and the casino or the one involved in creating the machine has to explain the whole mechanism of its winning rate or we can call it similar to RTP in the modern slot.

That goes on vintage slot machines but as always, the machine was designed to give casinos more profit compared to what users can take home, as that was what gambling is supposed to be. I hope we can find details on how the random algorithm works on vintage slot machines or how it follows a random result.