Do the rules in official Hoyle's books ever experience changes, major or minor?
For example, I have a Hoyle's Rules of Games from 1963: can I assume whatever content is in the book is still valid for tournament play?
Obviously any content added since will be missing (additional games, since-clarified irregularities, etc.), but I'd like to know if anything could now be potentially incorrect in my '64 edition.
It depends what you mean by "Official".
None of the games in Hoyle have an "official" governing body to set the rules. Or at least none of them did when it was first published. Hoyle attempted to fill that gap.
Hoyle attempted to codify the rules of many traditional games that have been played for many years, often centuries. Each part of the country playing to slightly different rules.
The different rules all still exist/existed and were not necessarily replaced by Hoyle, although it became common for players to agree to use his rules. Hence the expression - still used today - of playing any game "According to Hoyle". Such agreement does reduce the risk of arguments over the rules during play.
There is no mention in my 1980's copy of Hoyle of any rules of any game changing over time. None of the games in it could be said to date from after your 1960's version. So, assuming your tournament runs according to Hoyle, I would say your copy is just as valid as it ever was.
The 2001 edition of Hoyle's Rules of Games includes rules for Bridge, Cribbage, Gin rummy, Hearts, Spades Pinochle, Chess , Scrabble, and Canasta, all of which have tournament organizations that publish official rules. The laws of Bridge (both duplicate and rubber) have surely changes several times, most recently in 2017. Moreover contract bridge had official laws almost since it was created, and Hoyle's was never the source of those laws. I suspect that the official rules of some of those other games have been revised, at least in minor ways, since 1980.
In addition, Hoyle's includes rules for craps, Poker, and Chemin-de-Fer all of which are played at casinos that have their own official rules. Poker also has official tournaments.
