I know what you're saying, but this is a small business owner who I'm going to have to rely on in the future for any glass that I will need to replace when I'm restoring my windows. He's right down the street, so I'd rather not spoil the relationship. He's willing to make it work, and the measurement is only off by about a 1/2" width, which sounds like a lot, but it's 1/4" on each side.
"Brick mould" sounds like something fancy, but it's basically just the moulding you see around your door frame on the outside. He just finished putting that up and I'm pleased with how it looks. If I really wanted to go into full restoration mode, I would have had to replace the entire back door unit with its moulding and basically start over, but I'd rather keep the original stuff and just appreciate the way it has been adjusted over the years -- the door frame has been carved away to fit the previous storm door handle. The PO most likely put up the old standard size storm door, so that's what this guy was going off of. The painters took that down later on. I know, this guy should have measured the actual door opening instead of the door.
As I said, though, I'm thinking this was a blessing in disguise because the correct custom size square door probably would not have fit in my off-square doorway. This way the new "brick mould" frame is square and the new storm door (with pet flap!) won't have any functional issues down the road. And I still benefit from the lifetime warranties on the finishes of the door and handles.
EDIT: Here you go, here's a photo of the brick mould before painting. You can see how incredibly unsquare my doorway is. On the right where the handle will go you can see where the original moulding has been carved away in a semicircular pattern to make room for a wider storm door handle.
