One way to keep the order of pre-sewn blocks that works especially well for me is to use those little colored circles that are commonly used on garage sale items, etc.
I have found that if I place the tag in the upper left of each block - far enough in that it won't get caught in the seam - that it not only keeps the blocks in order, but keeps the direction too (put a little line under the number so you know which is the bottom - keeps from confusing 6s and 9s, for instance).
The numbering I usually use is 1-1 for first row - first block. So, if they all fall off the design wall at once, or you need to remove them for another project, when you pick up one with 4-2 in the upper left, you'll know that it's the fourth row, second block.
Works great when you have to jump to another project right in the middle. The tags stay on very well and reattach multiple times - just place them back on the paper from the package.
Saves a lot of frustration.
The alternative: Take a picture and reconstruct.
Either way, you haven't lost the design.