I actually noticed that, too. When they released songs on albums, sometimes they took the original version from the show, and sometimes they re-recorded it. But the album "Signs" was not the original release of "Exit", believe it or not. I think before that, it was released on a 45 along with "Count it Higher." And that song also has 3 different album versions. On the album "Letters and Numbers", it was the full version from the show, but without the crowd, which was re-released for the 5 LP box set "60 Favorite Songs from Sesame Street". Then it was also on "The Count Counts", but it was shortened at the end, because there was a public service announcement. That version was released on something called "25 Great Hits from Sesame Street", a Canadian release, I believe. Then there was the remix for the album "Born to Add". See, I think that sometimes 45s were previously unreleased tracks, but not usually. In fact, I just picked up a copy of the 5 LP box set called "60 Favorite Songs from Sesame Street", and it's great. It actually does have some tracks that were previously unreleased, such as "Danger" and "Proud" by Little Jerry and The Monotones", "What's the Name of That Song" by The Cast", "Special" by Bob, and "What Makes Music" a bunch of different people. But all of those were taken from the TV versions. But I'm wondering if the 45 version of "Exit" was the original version from the show.
Also, I think the album "Signs" was all new material. I think somehow, they realized it would be too hard to put some of them on the record the way they were on the show. The reason why you hear people's voices on "Exit" is because you can't see the people leaving. Same with "Telephone Rock", where you can hear the police officer talking.