could be just a different time it was made, how it was stored? when i buy nukes from play it again, they are more stable than buying from my local guy. leave it on your dash for a couple of days if you live in 100degree weather. it'll get nice and gummy, lose some stability.
just tune it...Bend it downward if you want it less stable..and bend it upward if you want it more stable...just don't do it during a PDGA Event because its illegal then. there are some good articles around the web about tuning discs if you look.
a big thing with nukes is the weight....is it the same weight??? also is it the same run??? Both make a huge difference. What I did to get mine beat in was simply hitting against trees on purpose or throwing it into the ground. I walked around for 2 rounds doing this and it was broke in perfectly. Tuning is also an option...but everyone I know that tunes their disc HAS TO tune their disc almost every round. It works though. I would also suggest throwing it on every hole...take an extra drive during those rounds that don't matter.
Ancient Chinese secret....put the disc in your dryer..VERY LOW or NO HEAT...throw in a towel or two...run for several hours....don't think about electric bills and stuff like that...you have a more important mission here.
as long as you tune it just a little and test it you should be fine..just keep doing it until you get it where you want and if it gets to flippy just tune it back up again..but your right ...it shouldnt be done to much...use moderation lol