I think you are OK in keeping/selling the items as long as you sent in a bug report to Neopets stating the extra items reappeared in your SDB. It might be a good idea to wait until you get a response from Neopets before doing anything with them, just to be on the safe side.
When my shop was rolled back two days in late Spring, I had items sitting in my shop that I had already sold--yet the items that I had put in during those two days were gone. I send a bug report in and got the reply "Thanks for reporting the bug, yada, yada, but we can't compensate you for any losses."
Since they sent me back a report and said nothing about "deja vu" items that had reappeared in my shop, I took that as a sign that it was OK to keep those those items that had magically reappeared. I figured that if they weren't going to compensate me for the lost items, that it was only fair that I be allowed to sell "deja vu" items--the gain from that helped lessen the loss that I suffered. And, I ended up selling the items and nothing bad happened to me.
Also, after the TP glitch last year, Neo basically said that it was OK to keep any items that you may have gotten by mistake:
"SITE UPDATE - By the way, we apologise about all the problems with the Island Trading Post. Basically, we had to rewrite it because there were so many trades the script that processed it couldn't keep up with the sheer amount of trades. When it came back up it went haywire and started giving the wrong stuff to the wrong people. We really are sorry but we didn't have any logs of what happened, so if you gained stuff accidentally - why not donate it to people who lost stuff?
"
So, personally I think it is OK to keep the stuff. However, I am not doing anything with my extra items until I get an email from staff at least acknowledging my bug report.
Tested made this fabulous set for me!!! Isn't it great?