I went to an international convention in 1973. They had a special program apart from the convention for the delegates, ethnic dancing and singing and costumes, experiences from the past during WW2.
It reminds me of Family Night (not to be confused with Family Worship) where members of Bethel auditioned and then put on a show inviting friends and family when possible.
Back then several congregations put together a musical evening with supervision from the elders. Shortly after than the curtain came down because of the "Great Apostasy" in the early 80's. No more "big" gatherings. We had sing-a-longs at one sister's house and I played piano and we sang many songs from musicals and pop standards. Had to keep it to 10 people but some still complained.
I still remember orchestras at circuit assemblies and district conventions...something also cancelled supposed due to the time it took.
So in 1978 the WTS said:
*** km 4/78 p. 6 par. 1 “Victorious Faith” International Convention of Jehovah’s Witnesses ***
Special music for the interludes and for audience singing is being prepared by the Society with the aid of many brothers throughout the country who are talented musicians. This means that there will be no live orchestras this year, but the specially prepared music will be presented by tape to give real unity to this important feature of the program at all the international conventions.