None. It’s not an operating system.
SPI was always quite good at issuing errata, and WRG in the old days would sometimes dish out free amendment sheets — my copy of their 1950-75 armour and infantry rules (the first edition) has amendments made from such a one. Most other companies never bothered.
The only time I can recall asking any rules questions was for GDW’s “Team Yankee”, whose rules were not as clear as they could have been, especially for a book tie-in game intended to attract non-wargamers into the sport. I got a very satisfactory reply. I also got a lovely letter from Bob O’Brien of the WRG when I wrote to him about “Seastrike”, but that wasn’t a rules query, it was a note saying what a brilliant game it was, and suggesting a couple of extensions.
I suspect I am not alone among gamers of my age and weight in buying rules and games largely to steal ideas from, rather than necessarily to play.
All the best,