I see frogs_fan. Playbill lists 4,971 as of April 13, but IBDB lists 4,963 as of April 20. I wonder if Playbill is including the 16 previews as part of the tally? That would account for the discrepency. If so, they are wrong, you are right and that puts the 5,000th on May 24.
Either way, we still don't know if anything special is planned.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com