Recently, I purchased jelly rolls from JoAnns. When I started working with them I noticed that some were not an even width all the way down. Some "zig zagged" along like they were folded and not cut perpendicular to the fold. Some had ragged edges because the fabric was creased and was not straightened out before cutting. And that was all in one jelly roll!!!
I called Joanns, and even though I had already started sewing some of them together (tube quilt), they took them back and gave me a full refund.
So, before you start using them, lay them together and make sure they are the same sizes and straight!!