Edith stopped wearing glasses in the later years.
Gloria developed a New York accent in the fifth season.
Mike's mustache is missing in The Boarder Patrol, which airs before Archie's Chair, which is the one when he shaves it off.
Irene is Edith's best friend, but she disappeared without a mention.

Betty Garrett told me in person that her part didn't get enough on-screen attention, and even though it was fun, they didn't want to. Her name was not mentioned once in the following season.

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Andrew Carden

>>Mike's mustache is missing in The Boarder Patrol, which airs before Archie's Chair, which is the one when he shaves it off.<<

I'm convinced that there are a few episodes around this time where Rob Reiner was wearing a fake mustache. It's as if he shaved it off, and the producers had him wear a fake one until they could figure out what to do. I'm speculating, of course, but Rob definitely looks a little different in a few shows.