There apparently was some confusion and errors regarding the Chaos Space Marine Limited Edition Codex. I wont go into all the details, as the info below very clearly describes the confusion when two books showed up with the same limited edition number on them.
via Sharp1011
http://www.reddit.com/r/Warhammer/comments/119a29/there_are_multiples_of_the_same_numbered_ltd_ed/
A friend of mine bought the Limited Edition Chaos Codex which was $100 and limited to only 1000 copies. He went and picked it up on Saturday and was content. He was even happy that he managed to get #127 out of 1000.
Then on Monday he goes to check how much they are going for on Ebay. In his search he happens to find a listing for one that claims to also be #127 out of 1000. Thinking it's a scam he contacts the seller. The seller is also surprised and sends him a picture of the number in his book. Both are #127!
Here are photos of both copies: http://imgur.com/a/2csqE
So my friend is understandably upset and contacts GW to see what the hell is going on. GW's story is this:
Apparently at the last minute they decided to change the numbered paper inserts. Apparently something was wrong with the watermark and they decided to remove it from the cards. Unfortunately they already put them in all the books, shrink wrapped them and sent them out to the various countries. 400 was sent to North America, 400 to the UK, and 200 for the rest of the world. So to replace the cards they had to open each one, remove the old card and put in the new one. Apparently this was done properly to all the NA copies, but the UK didn't and just taped the new card on the outside and left the old cards on inside cover. They also messed up because they didn't replace the cards with the same numbers, but gave each book a new number with the new card.
So according to GW, my friend has the "real" #127 since it doesn't have the watermark and the dude in the UK has the "fake" #127. This all sounds like stupid to me and I'm sure they would tell the UK guy he has the "real" #127 if they contacted him.I'm not sure if GW is telling the truth, but there is at least one guy on the B&C saying he received two different numbers in his copy... so who knows.
EDIT:
I just found out that the seller of the second #127 codex found his 'real' number in the trash. Turns out he's actually #799 and updated his ebay auction to reflect that. This is confirmation that people in the UK most likely received two numbers with their books, the one on the outside is the 'real' number while the one on the inside is the 'fake' number.