[78-L] Single-Sided Columbia - microphone label

[Tyrone Settlemier]

I'm looking at a single-sided Columbia of Lincoln's Gettysburg Address.  No, it's not by Harry Spencer, but this is a CBS/Microphone Masterworks label by Charles Laughton.  It seems to be in their M-suffix series, but it has an S prefix, i.e. S271-M.

(matrix is CP 253-2)

So, does this fit into their regular M-suffix masterworks series?  Does the "S" stand for single-sided?

Actually, it's not quite single sided.  The reverse has a lead-in groove, six silent grooves, and the rest of the record consists of runout grooves and the eccentric end grooves.  Matrix number for this side is 33451.

Can anyone shed some light on this one?

Thanks!

Tyrone