With the showing of tonight's ep, all of the prior years' Seinfeld's will have been shown at least once in syndication. It's interesting that they timed it so that the current season has just ended...it'll be interesting to see how long before any of these eps turn up in syndication. Probably not until at least September, since NBC probably still has the rights to show them during the summer.
BTW, I've read a bunch of people here say that they were so shocked...SHOCKED by the way Susan's death was handled that they will never watch the show again. Yeah, right. You'll all be watching next September, just like the rest of us.