Couple of small points:

Country western (and jazz and blues) 78 rpm's from the early days of recorded music listed one side as an A side and the other as a B side.

Starting in the 50's-60's you sometimes get the same song in stereo on one side and mono on the other.

In digging through old 45's, you'll often find a radio station copy with a hand-written note from the station to play a certain side. If memory serves, it tends to be the same as the A-side, but the station wanted to make sure the DJ didn't accidentally play the B-side.