I would measure the narrowest strip and use that as the determining factor in the block size. If this is the quilt I am thinking about, the block size is very forgiving. The size of the finished quilt will be a bit different, but you can fix that with borders.
Incidently -- the jelly roll batiks you get at LQS also have this problem. The best thing to do if you work with jelly rolls is make sure how wide the strips are before you start. (Some of the edges get frayed on some jelly rolls so again, not all of the strips are the same width).