FYI, I've received a copy of the Rummikub rules for "The Official World Rummikub Championship" (WRC 9 Berlin Germany 7-10.11.2015)
Intriguingly it has these rule differences from the standard Pressman rules:
The joker can be used to represent any tile. During a turn, a player may retrieve a joker from the table by replacing it with the tile it represents (from his/her rack or from the table), and must use the joker immediately to form a new set (or sets)
A set containing a joker may have tiles added to it, or it can be split apart in the usual manipulative way. If thereby freeing the joker, it must be used in the same turn as a substitute for any number in a new set. At least one tile from the player’s rack must be used on the same turn.
Should one get 3 "doubles" (2 of same number and color) before the game starts, he can request a fresh start for all champions sited at his table
(NB for some reason their rules are entered entirely in all caps, so I had to convert them.)
I'll try to upload the file I have but I gather it could take weeks. It does not seem to be online anywhere. The closest version is this one from New Zealand: