Like you, I took note of the "punching in" the end of "Blue Canadian Rockies" in the Studio B film.

Always wondered how they did it with tape recordings.

It reminds me of one, or possible two, recordings where a possible alteration is noticeable.

I haven't checked yet, but the most prominent one in my memory was the "Hawaiian Wedding Song" where one verse near the end seems to come a little too fast.

I could be wrong here just an observation.