Can you trust your long jump PR?

Your point is valid but pits that are a foot lower than takeoff can not be that ubiquitous and surely rare at stadiums and fields that regularly host meets broader in scope than HS dual meets. Granted I have not been active in officiating HS meets of late but I can not see any officials organization not correcting pit discrepancies of magnitudes over 2 inches.

A big drop at the end of the runway may mean the officials took material from that area to bring the actual landing areas up to level. As long as the, lets say 15 foot to 30 foot zone, is level with the takeoff board who cares if the none landing areas are low? The fix is simple if your homefield pit is low--fix it. Olympian Norm Tate used to double dig the sawdust or sand pit as part of his normal warm up routine .

The deep pit phenomenon likely doesn't occur at major USATF meets, but certainly seems to occur in high school meets, including some region and state championships. What are peoples experiences in different parts of the country?

The active landing area needed for a range of abilities for boys/girls long/triple jumping can span a good portion of a pit, so it is difficult to address by shifting sand around. While individual jumper may want to soften their landing area by digging up a pit, they are not going to go out of their way to raise it to ground level.

Filling a full 24'x9' pit with the 4 inches of missing sand displaced by covers requires addition of about 72 cubit feet of sand (4.3 tons), so this is not a trivial exercise and needs to be done on a seasonal basis, with provision for off-season sand storage.