I used to work in fine art printmaking. The weird thing about signing blank paper before the prints are done is that usually not every print in a run will make

I used to work in fine art printmaking. The weird thing about signing blank paper before the prints are done is that usually not every print in a run will make it into the final edition. If you are doing say an edition of 100 prints, you will maybe print 130-150 of them, and then choose the 100 best ones to actually publish. This gives leeway for misprints and imperfections. Prints are ususally numbered by the artist when signed, so presumably Dali would either have not been numbering these and having the printmaker number them once the final prints in the edition are determined. That, or he was numbering them and they just didn't have the same quality-control that a typical edition would have.