The "invention" of stereo recording remains an issue to this day.
Almost parallel with Blumlein's claims was a notable series of experiments
done by Western Electric/Bell Laboratories in conjunction with Leopold
Stokowski and the Philadelphia Orchestra in about 1927.  These recordings
were produced using a variety of techniques of direct disc recording
featuring the 45/45 system (later adopted in the mid '50s in microgroove
and sanctioned by the RIAA as the existing standard) and other various
experimental hill & dale/lateral methods.  (Magnetic tape recording was
invented by Telefunken in Germany in 1935.) LP reproduction of these
experimental recordings were made available for a short time in the early
'80s by the Telephone Pioneers of America (retired Bell Labs people.) I
do not know of any current source for this material.  Much of this work
was done by Bell Labs in conjunction with their extensive development
of basic audio and reproduction devices including motion picture sound
recording, dynamic loudspeaker mechanisms, microphone development and
electrostatic speakers.  This was a period of explosive audio engineering
development on both sides of the Atlantic.  Westrex, a successor company
to Western Electric/ Bell Labs produced the first commercial 45/45 stereo
record cutter in 1956 in commercial quantities for the record industry.

Blumeline gets much credit for evolving several methods of microphone
pickup which remain evolving commercial standard technology in use today.
The source material for this brief review came from various magazines
and texts published over the past two decades.  The most recent I can
recollect was published in the now defunct AUDIO Magazine.

It's been said that "...there is nothing new under the sun." The basics
of stereo recording go back a long way, indeed.

Bernard Gregoire
Hingham, MA