The first song book I remember had a green heavy-paper binding. That must have been the "Songs to Jehovah's Praise" song book (1950). I was piano player using that song book at our KH, and I recall it had some nice songs. At the last international assembly held in NYC Yankee Stadium and Polo Grounds (1958), there was an orchestra and choir who performed some very sophisticated and beautiful songs that were subsequently performed at district assemblies for a few years thereafter. The melodies were beautiful, but some of it had some unusual lyrics.
At the time I often accompanied a pioneer JW who was a musician. He was a jazz pianist who played in local night clubs with two others, which allowed him to pioneer during the day. He told me that the orchestra leader at MGM was rumored to be studying with Jehovah's Witnesses and that he may have had something to do with the special musical arrangements presented at those conventions. For whatever reason, those musical presentations at district conventions ceased about the time the 1966 song book was released.
I remember trying to play the music in the new book--it was very difficult because the melodies were not as intuitively normal as intuitive as most are. It seemed the new songs were written by amateurs. They were difficult to play and difficult to sing. The singing at the kingdom hall dropped significantly because people could not seem to follow the tune, and neither could the accompanyist (me). I missed the better songs in the previous song book and wondered why they were replaced. It was soon revealed that it was because the songs had not been written by JWs.
I became inactive a couple of years later, so I wasn't around when I heard they switched to not having a piano accompany the singing, but it didn't surprise me.
Anyway, that's my recollection.
~Binadub