From the members I have conversed with, they are forbidden from using caffeine.
> It took a great deal of time, repetition, patience; no small amount of hope and faith; lots of reassurance from my wife; and many liters of a diet soda that shall remain nameless.
[0] https://www.churchofjesuschrist.org/study/general-conference...
That's speaking of teachings and doctrine, of course. When it comes to history that's less like trying to nail Jell-o to the wall and it's much easier to find sources for more accurate history, and I agree that it's a bit sad how little accuracy in history seems to be respected by some believing and formerly-believing members.
The type of thing I had in mind are things that aren't ambiguous but rather are pretty clear. Things like "the actual edicts ... aren't really supposed to be published or talked about" regarding caffeine/word of wisdom. I certainly don't claim to know everything, but I have spent an insane amount of time reading/researching Mormon history and I've never heard that before. Stuff like that seems to pop up constantly for some reason when I talk about things with ex-mormons.