Sandi
Not to be confused with the previous Sandi, this Sandi has a whole different story — when she introduces Jerry to her roommate, Laura, Jerry gets caught up in the idea of trying to switch between the two. He and George come up with an insane plan to accomplish the coveted switch by having Jerry suggest the roommate joins the pair in the bedroom.
Sandi in this gag-worthy storyline is played by Jann Karam, who hasn’t managed to land any big roles since. Her on-screen appearances are few and far apart, and the latest one was in a small road-trip movie in 2016, which leads us to believe she has since been investing her time in non-acting endeavors.
Gail
Actress Anita Barone plays Gail Cunningham, a woman who has dated Jerry three times, all the while refusing to touch him. Normally, there would be nothing wrong with that, only she kissed Kramer after he walked her home one time in the episode "The Shoes".
Not many people know this, but Anita was the original casting choice for Carol, Ross's lesbian wife on "Friends", but only did it in one episode. Don't worry about her, though, she got other recurring roles in other TV shows — most recently as Sabrina in "Brew Brothers".
Sandi
Okay, so this one is for die-hard fans. Actress Elena Wohl, who appears in "The Pilot" is hired to play an Elaine-inspired character in Jerry's self-titled show. It is the ultimate frame-in-frame loop that ends up in her convincing herself she and Jerry are actually dating.
While actress Elena Wohl did have recurring TV roles in her pre-Seinfeld days, she hasn't really had any memorable ones after. Maybe it's the show, maybe it's showbiz, and maybe she decided to focus on other things.
Laura
One of the several Lauras decorating Jerry's love life is initially introduced as the roommate of another love interest — Sandi. When Jerry purposes all three of them have a... let's call it "adult sleepover" together, he's surprised to find out they are on board, and that the thought of going through it is making him uncomfortable.
Actress Heather Medway plays Laura in that episode ("The Switch", 1995). She has only had one memorable role since — Cameron Westlake in the TV series "Viper", but she quit acting altogether in 1999, two years after having her first child with writer/producer Danny Bilson.
Shelly
In "The Doodle", Jerry and his designated girlfriend Shelly go out on a double date with George and his own designated woman. The incredibly random reason for their breakup is him refusing to use her toothbrush upon finding out he's left his at home, which was being fumigated for fleas.
Dana Wheeler-Nicholson, who plays Shelly, has done a lot since her part on the show. This could be why you're scratching your head trying to understand where you might know her from. If that helps, her latest big roles are Beverly O'Connor on the musical TV show, "Nashville", and Angela Collette on "Friday Night Lights".