Too many retailers use the non-discretion route... if you added custom rims then good luck doing anything with those box checkers.
I once brought by 70s c20 in for tires at costco, special ordered online with the instant rebate plus penny installation deal. When I got it there they tried the old "that's not the size" routine... problem is, door sticker called for bias ply in the old sizing numbers on a 16.5" rim - both of which are basically phased out.
Ultimately, the fact the truck was older than the computer could pull, and the fact the truck was still running chevy poverty caps, just a newer 16" size, guy just went with it. (I think mostly to avoid having to deal with returning the tires and refunding me)