Back to J.S. Bach's original question, I recently picked up some 78 sets at a local thrift store, and one 5-record RCA Victor set has one record with EXACTLY the same embossing as in J.S. Bach's photo. I thought it was cool too, and it was immediately evident it was "filler" (in this case, side #10)for a musical piece that filled only 9 sides of a 10-side album set. If you stare hard, you'll see the embossing has a fast-spiral groove to the center so your automatic changer (Capehart 16E anyone?)would bypass that side quickly and go on changing records. I don't know when, or for how long, RCA Victor did this. Maybe somebody can date my sample, RCA Victor DM-705, Beethoven Concert in D Major, Op.61, Jascha Heifetz, violinist, Arturo Toscanini and the NBC Symphony Orchestra.