Well my 73 jazz has the gasket fitted but I know some didnt. Not sure this wasnt just down to lack of quality control at the time in the 70's. There were also quite a few oddities escaping from the factory at the time as well. On the production line if a techie ran out of the particular scratch plate for instance they would just fit the nearest one to hand and so some unusual examples were released. The main thing for you to watch out for if you are looking to buy, is the neck fit. By the early 70's the jigs for cutting the neck pockets were rather worn and the pockets tended to be larger than they originally were. Generally you can move a fender neck of this period from side to side in the pocket. That doesnt mean you should take a walk though. You really just have to treat it with care and make damned sure that the feel and sound is right before you buy. The most common problem to check for is the 'C' on the fifth fret of the 'G' string. They can tend to be dead, but not all are like that. Personally if was dead I'd walk, but otherwise if it was live as it should be, there is no reason not to buy.
Hope this helps. Good luck.