When I was junior-high age, our music book had at least two medleys of popular songs of old, probably Tin Pan Alley Tunes. These medleys consisted of the best parts of the old songs, strung together like beads on the necklace.

I think "I've been Working on the Railroad" is a medley of two or three songs put together, just like the medleys we sang in school. The Dinahs are entirely different things. The first Dinah is a locomotive and the second is a woman in a kitchen.