I know that the first intentional NS comp LP was put out by Pye here in the mid 70's ... but I would suggest that before that a few comp LP's had escaped in the US that would (if they were 70's releases) be classed as releases aimed at the NS market. Here's my tip as a probable 1st NS comp album ... compiled by Philly / New Jersey radio / TV DJ Jerry Blavat.
It was released in late 67 and featured 20 tracks in all, of them I'd say 16 would count as NS cuts -- The Jerry Blavat TV Song Storybook (no label identified on the record or album sleeve but 95% certain a product of the Lost Nite label / Crimson Records). Jerry was part owner of these record companies, so it makes sense that 'his' LP would be put out by them. As Crimson were releasing new product by the likes of Lee Andrews & the Hearts, Soul Survivors, Damon Fox, Brothers Two, Chuck Trois & the like at the time, he obviously was aiming his product at teenager dancers who loved soul stuff.