Here's a comment from Aine Mulvey, who has unearthed scholarly work of Hamilton Harty, who used the term "collaborator" all the way back in1930:
Hi, I'm an Irish Ph.D. student, currently researching Hamilton Harty, who was a leading accompanist in London in the early 1900s. He disliked the term 'accompanist' and wrote a paper on 'The Art of Pianoforte Accompaniment' in 1930, in which he argued that 'collaborator' would be a more accurate term. I think it may be the first use of the term... I was curious, as it hasn't really caught on over here although I've heard it used in conservatories in the States and in Italy. I was doing some internet research to see if there was an earlier mention of the term or if Harty coined it. I think he pre-dates Samuel Sanders?What about the first mention in the New York Times? A quick search on the Times site reveals that the first NYT mention is from none other than Joseph Horowitz in a 1978 review and is in relation to not Samuel Sanders, but Albert Lotto:
The program also included the Debussy sonata and Brahms's Trio in B (Op. 8). Albert Lotto was the strong, richly collaborative pianist in the Beethoven and Brahms works, and Carol Stcin Amado was the capable violinist.It seems to me that Joseph Horowitz's words are in regards to how well Albert Lotto played in the ensemble rather than what he did for a living. But might Samuel Sanders have come across this article and might Joseph Horowitz's wording of this review have influenced Sanders' eventual desire to rebrand the accompanying profession a year or two later?