Yeah, kit makers make mistakes, too. All the good ones will fall over themselves to get you fixed up. But that's why I have the stock of wood that I do. As long as it is stick or a little sheet stock, I just replace it out of my stock and drop the maker a line to the effect that they had a an error, to help them track QC. But it's pretty rare to be short much. Usually it turns out to be my mistake.

Plus I replace a fair amount of wood in kits with lighter ot straighter stock, depending on the quality of the kit.