Author life plus 50 doesn’t apply to these older works, only the 90 year rule extended by Disney And congress.
I understand that the original work isn’t extended by the revisal, but the revisal (depending on how big) would have its own copyright. Once the original copyright work is in public domain, there is no income left (which I assume is a large concern for r&h estate). But If revisals are made like flower drum song (which sadly flopped) were in demand, then copyright of those pieces would continue bringing in income to the estate. This Oklahoma might be more staging than actual rewrite of script.