Guys im telling you it wont matter because gamestop internally knows how many 3ds systems they will get. if you pre order, you get one period. But be forwarned, if they did not and they over reserved, you think if you were pre order number #3 and they only got 30 units instock and you were 45th in the line on launch they would save you one? it dont work that way. too many people got burning with the wii and another games as such in the past.
If your store does take that time to go through the receipts on the computer and number them before launch, kudos, your lucky.
but it wont even matter, everyone who pre orders before they cut it off will get a system.