There were two separate N7's; however, I never saw anything but rumor about various versions of other devices. I don't recall any rumors about N9 varieties. The N9 seems to have "good" and "not so good" production results that have not been correlated to specific runs.
Thanks, I think they corrected some issues early on, but other than that there doesn't seem to be a way to tell if you buy a mildly troubled one or not. I probably should buy the one that is slightly more with a 60 day return to make sure.
Thank you
This is excellent advice for yourself as some issues didn't show for at least 6 weeks of usage.
This is the thread about possible revision: http://forum.xda-developers.com/showthread.php?t=2961927
Some are adamant that HTC tweaked the production to improve the device. FWIW, mine is a "pre-revision" run (Oct 18) that never had any of the problems mentioned (others have reported the same). It has problems which are probably a combination of hardware/software limitations. N dp5 seems to be working really well, but it's only been a week. The problems show up after about a month and are solved by wiping/re-installing.