Two historical questions regarding (1) medical timeouts, and (2) the frequency of changing to new balls.

I'm curious but...

When did medical timeouts begin on the ATP tour? I don't recall a single medical timeout in any match I watched during the '70s or '80s? (I stopped watching tennis for about 25 years.) Were they occuring and I just didn't see them? Or were they just much less frequent than today? Or were they not allowed at that time?

Has the frequency of changing balls (after first 7 games, then every 9 games) in ATP tournaments been the same since the '70s? I don't recall them being changed that often back in the Dark Ages but that could just be my geriatric brain at work.