As much as I'd like to know more about the various studio orchestras for record labels, it's shockingly hard to find any information. Even the antics of the Wrecking Crew in the US shows how many musicians cycled in and out with information missing from the work cards amidst the sheer number of anonymous backings of hit songs. I can only imagine the record keeping for library music labels.
Though the International Studio Orchestra seems to have been part of the old guard of library music as described in this bit about KPM's Group Forty Orchestra which performed similar material.
That was 1967. The whole business of library music was changing. A new style was coming in. And the man largely responsible for bringing those changes about was Robin Phillips. When Keith Mansfield first arrived in the copyists' office in 1964, Robin Phillips was the post boy. His father ran the company and Robin was working his way up from the bottom. In those days, library music was mostly light orchestral music or trad jazz.
Adrian Kerridge, who engineered most of Phillips' jaunts to the continent from the late sixties on, remembers Robin's predecessor bringing the Ted Heath Band in to Landsdowne Studio, the Holland Park recording house where Kerridge used to work as an assistant to Joe Meek. The silken strings of tracks like 'Limelight Waltz' and 'Pink Fizz' by The Group-Forty Orchestra, KPM's other stalwarts in the late 50s and early 60s, sound like another world, sepia-toned and chalk-striped. "It was a good library," as Mansfield said, "but it was second division." All that was about to change.
I have Mood Modern book on order which hopefully may shed some light on pre-1965 library music material.
But studio orchestras seems to be part of the older trends, maybe part of the early catalog released on 78s such as:
De Wolfe - International Studio Orchestra
KPM - Group Forty Orchestra, Group Five Players, Group Ten Players, etc.
Synchro - Grosvenor Studio Orchestra, Paris Studio Orchestra
Brull - Harmonic Studio Orchestra, C Brull Dance Orchestra
Southern - Westway Studio Orchestra
Bosworth - Bosworth Orchestra, International Radio Orchestra
Chappell - Queen's Light Hall Orchestra
Boosey and Hawkes - New Concert Orchestra
Pre-60s library music is niche upon niche, it seems to be.