[78-L] Columbia Add-A-Part records.

[Royal Pemberton]

What is the story behind the Add-A-Part series of records Columbia
offered?  For years I've seen them listed among the different series
or records, and the prices per disc, on a handful of sleeves or albums
from the 1940s.

I have one of them.  Early 1940s blue (a la Masterworks) label.
Catalogue number 65116:  it's Strauss's BLUE DANUBE (in two parts)
performed by 'Members of the Rothschild Ensemble'.  The labels state
'Piano missing/EASY', which leads me to believe the A-A-P series were
precursors of Music Minus One and such like educational products.
(There is no information on the labels as to what special piano sheet
music or instructional literature may have been designed for use with
this record.)

Both sides have a brief outer track with a violinist playing an A
natural, which ends in a locked groove.  The music tracks include two
baton taps before the ensemble begins playing, as a cue to the
pianist.

Matrix number for side 1, 021991; no lead in spiral.  Leadout spiral
ends in a concentric groove like some 12" Telefunken 78s I have (and
whose matrix numbers appear to be in the same series).

Matrix number for side 2, XCO 25954 (dub).   Tuning track has lead in
groove.  Music track has no lead-in groove, and has typical machined
leadout with mechanical eccentric end typical of US Columbia records
of the 1940/1941 period.

Any information on this record, or the series as a whole, greatly appreciated.