Did I Screw Up OR Get Hosed???

I bought a front driver's side armrest off of ebay. The listing said it was off a 64 270 convertible Dart, and I assumed it would be the same as what came with my 64 GT convertible Dart. It turns out this armrest is 1.5 inches shorter than my passenger side (10" vs. 11.5"). Was there indeed a difference between the 270 and GT armrests, or was the description wrong? I need to know wheather I should be mad at the seller or myself. THANKS!