Sorry about that - I'll blame it on my evident decrepitude. Just slack of me not to check all the numbers properly.
There was an issue of Wilfarht as one of the discs in Decca Album A-833 Favorite Polkas, Volume 1 advertised on 9th June 1951 in Billboard: -
I see that Wilfarht had an album all to himself as No. A-555 in 1947 as by this period in his career he was being recognised far and wide. There seems to be an enormous number previously recorded material repackaged in albums at this time (mid late 1940's) in the US, and I can think it would be only natural to review older recordings, say by Wilfarht's, to see if they could be marketed again.
So would a good conclusion (for now) be that these discs were pressed in order to see how, or if, they could be re-bundled into Albums?
Still leaves the 'L.M.' question hanging there for the moment!
I did find an image with a label that looks as if it is taken from the same source outside the Internet Archive which claims/suggests that this label is an LA Test Pressing http://inkspots.ca/INK-SPOTS-78-RPM-RECORD-LABELS.htm (see foot of page)