Looking at the magic that happens as you open the cartons, I see a number of items that make me think... 

"Did they cheat in the 50's & 60's when they did not have quite enough to make an album"?  Releasing an EP may have been an easy way to keep the artists in full view, allowing extra time to finish the writing and recording of the next album.

Then, I look at today and note many of the songs released are done individually, or as an EP.  Digital streaming means there is no need to prepare an album now, so maybe the originals were just leading us to the way of the future, even though we could not tell at the time.

Here's a few from then to whet the appetite...