The careful and cautious wording in the citation is necessary because there was a simultaneous effort in New York at Bell Labs, by a group including Arthur Keller, I. Rafuse, and their supervisor Harvey Fletcher. They too achieved stereo recording in 1930-1931, and then they set up their equipment at the Academy of Music in Philadelphia, home of the Philadelphia Orchestra and its conductor, Leopold Stokowski, and with Stokowski's cooperation made over 100 recordings of the orchestra over the course of the 1931-1932 season. While many of these recordings were done in wide-range (i.e. high-fidelity_ mono, some were done in stereo. For Details see
Robert McGinn, "Stokowski and the Bell Telephone Laboratories: Collaboration in the Development of High-Fidelity Sound Reproduction" Technology and Cultue Vol. 24 No. 1 (January 1983) 38-75.
Thus, while Blumlein's is a milestone-worthy achievement, claims like " forthe first time" are unjustified. It seems a case of simultaneous invention.