I have on average 8 machines a day that will drop page counts. I did consider the NVRAM reset at first but we've proved it's not this. Also, with some many doing this daily i think it's highly unlikely to be this.
I know you say that you have never seen this in 20 years but i have alot of evidence showing that it's is defitnely happening.
I don't see the issue at all in other makes, just the HP Laserjet.
I believe unless you are actively looking for it, it's very hard to spot. For example:
Printer has 100 prints on the clock
Drops 10 prints - down to 90 prints
User printers 11 pages
Count is now at 101 - which technically is a posative count - however the page count should be 112.
I have times when it drops a few pages which you would never spot unless you were aware of the issue.
The only reason i spotted it was because we had a massive drop on one printer that we were auditing.