MrWCF: It's called "Portable Game Notation" as though it applied to any game, but it doesn't. The definition is for chess only. It's fairly recent. As far as I know there's no regulating authority, so you can extend it any way you like, but then, of course, there's no guarantee that other people who develop the same game will use the same convention. Just for example, to extend to loop chess you need a "parachute" symbol, which has been taken as '@'.

Checkers, for example, use an entirely different notation, and as checkers is fairly established I see no chance (or reason) why people should switch to PGN.

By all means, define a PGN for camelot, it's not difficult. The move notation used here and on http://www.worldcamelotfederation.com/ can serve as basis, just add tag definitions and don't forget a "variant" tag!

See http://en.wikipedia.org/wiki/Portable_Game_Notation for it's history.