Hogan’s Heroes had the same opening, with the same easily identified opening them music, for five seasons, until Ivan Dixon left and Kenny Baker replaced him.
No, the montage changed after the first two or three seasons. F’rinstance, Newkirk went from shuffling cards to cracking a safe; Kinch, from raising the antenna to tapping the Morse key.
Corner Gas ran for six years and never changed its opening.
The music and the title sequence did change - the music to a sort lush strings version of the same tune, and the titles to a full-colour version (it was originally in blue and black). The reworked music was unpopular and didn’t last, reverting to the original, but the colour titles stayed (and yes, the dome can be seen in them now).
The Eastenders title sequence has been changed more than once. The Millennium Dome was added, then there was this revamp:
https://www.digitalspy.com/soaps/eastenders/a175106/video-new-eastenders-opening-credits/
The Olympic park was added in 2012 as well.
The Big Bang Theory almost qualifies, excepting the cast shot at the end.
If you just downloaded them from a torrent or something otherwise unofficial, they very well may have been “ripped” from syndicated versions. If you got them from some more authorized source, well, even then they could contain the edits. Sometimes they’re pretty sloppy/lazy about what cuts wind up on DVD (or downloads in this case) and it’s not always even consistent across different seasons of the same show.
I watched ER for most of it’s original run, and yeah, there were definitely different, longer credits in the earlier seasons, with alterations along the way to go with cast changes, as burpo mentions.