The first four letters matter to most. Vudu regulates the codes, so knowing the first 4 letter, will allow bidders to know if they will work on their account.
I must not have been clear. I'm sure the codes are good. But the first 4 letters dictate how many of that code can be entered per each personal Vudu account. Meaning if someone has already put 5 codes in (with the same first 4 letters) they can no longer redeem any other codes with those 4 letters via their account. This is only for special pricing codes, like the ones listed (ie not movies).