Since we have no full contemporary description of the game, there are many possible variations. Sources often differ in details, and are sometimes contradictory. In some cases, a given set of rules is actually unplayable in practice.
Our Rules of the Game are not intended to be definitive. They are, however, straightforward and lead to enjoyable play.
It seems reasonable that there has always been variation in the rules, and their interpretation; just as modern games of all kinds have variations and ‘house rules.’