Why does Mission: Impossible sometimes use a shorter intro?

While rewatching the 1988 run of Mission: Impossible I noticed that in some episodes they used a much shorter version of the whole intro sequence, which had a shorter music piece, less pre-character clips and a shorter character introduction. I think this happened for all 3 versions of the intro (Season1-Casey, Season1-Shannon and Season2).

Now the only reason I could imagine for doing that might be to adjust to a variable length of the actual episode. But this could as well be solved by varying commercial breaks or adapting the entire episode itself, afterall we're not even talking about minutes here. I am also not sure I've ever seen another TV-show employ such a measure of short intros on seemingly irregular episodes. Or maybe there even is a pattern of why exactly those specific episodes use it that just eluded me.

So is there any official information or strong evidence why some of the Mission: Impossible episodes employ a much shorter intro sequence? Was it really just to adapt to a varying episode length or was there more to it? In the former case it would also be nice to know if this was actually a common technique in TV production.