That may account for the "full orchestra" sound on "Papa Was a Rolling Stone" with shimmering strings, a harp and brass. The small quarters of the Motown facility just seem too tiny for everyone to fit in a confined environment. As for the string section in particular, were they likely rented from the local symphony or did they have such players on the staff? Multiple violins were featured on Motown songs of the 60s and early 70s such as "Love Child" and "The Happening" by the Supremes.
“were they likely rented from the local symphony “
Yes. In a way. They would have been hired as private contractors, not “rented” from the symphony. Symphonies don’t actually own the rights to the musicians they use. Just because one is a “member” of a symphony orchestra doesn’t mean they can’t do any other gigs they choose to do. Check out Martin’s book. Great easy read about a fascinating gentleman! Covers all facets of recording, in layman’s terms. I’ve read it twice,,,, so far!