Welcome, GM.
As Mark said, there is often some variance in the length and width measurement of posters. For the vast majority of cases, it seems to be less than 1/16", with some formats often almost identical and not close to 1/16" difference among copies of the same title. It was smart to measure the borders, to see if those had been trimmed on your copy. With the popularity and relatively high price of this title, it would probably be more likely to be reproduced, and it's wise to be cautious with purchasing, selling, etc.