I've been doing this aviation thing for 30+ years now. It seems to me that for the first 15 of those years the rules and RT phraseology stayed pretty much the same, but for the last 20 years I struggle to keep up with the changes.
I used to give "maintaining X thousand" and "left Y thousand" calls to ATC. I think it was a requirement.
Now I only verify altitude/level when asked. I give a "maintaining altitude/level" or "cleared to" call to ATC on frequency changes, and when told "when ready descend to altitude/level" I read back the altitude/level and descend when I am ready. I no longer give "left altitude/level".
Seems to work OK and I don't get yelled at by ATC.
Dr