There is a very subtle difference in the 3K & 10K issue of SC#5172 (USA-Star Non-Profit)
The bottom blue border of the 3K roll is 1.5mm wide while the 10K roll is 2.0mm wide. This would be helpful for those collecting used stamps (and we all get a ton of non-profit solicitations through the year)to differentiate the issue roll of stamps (3k vs 10k) without the little notation on the packaging. It is noticeable when side by side but singles not so. Just an FYI for anybody collecting varieties. BTW Scott does not differentiate (yet).