I think PRs are whatever you want them to be. In my opinion they are used for motivation to try and exceed your previous best lifts. However, if you are finding that 20 year old PRs are something that is causing you to be unmotivated or frustrated, then banish them and work on hitting current PRs.
No one is going to audit your workout logs for accuracy. If you squatted 500 in 1990, took 20 years off and are damn glad to finally make it back to a 315 squat, then that's something to celebrate. Not feel down because it's not a personal best.
Call it a 22nd century personal best or something, whatever makes you feel good about yourself and your progress.
I am Anton Zdravko Martin!
Best meet lifts: Sq 150 Kg (330 lb), Bench 120 Kg (264), DL 160 (352) @89 Kg (197)
Best gym lifts: Sq 375, Bench 280 (pause), DL 385 @205 or less
Goals: 3/4/5 while healthy and fit
"Hack away at anything which isn't essential. Do what you love, and do it often." Fazc.
"Everything competes for recovery so more assistance is not always the best idea." miked96
"Squat:15 sets of 3 with 150Kg
Deadlift:15 sets of 3 with 150Kg
It's not rocket science." Big Swede