Not sure if this is true, you can see that on any device with pressure meter (basically all 'smart' watches and phones), the standards are 2000-2500m altitude. Once you can create an altitude X inside the plane, you can do say 70% of X too.
Maybe just your condition improved?
New composite ones like A350 and Dreamliner have cabin altitude of ~1800m
Higher humidity too.
I don't know. My bottles of water aren't completely flatten when we land, something that I remember was always the case. Keeping in mind flying in the 90s means taking planes manufactured in the 70s and 80s (including a Caravelle!).