Back when Guild transfered building to New Hartford, CT some egghead decided that acoustic guitars did not need an additional strap button, but that electric/acoustic guitars did. That said, my F512 came without one
"We" had a contact there that rectified that!
Seems very weird your Starfire came without one, as
@Default said, a QC miss. The position does seem correct, if it were a Gibson or Epiphone, but I agree with you, if it just doesn't feel right...
I would caution however, not knowing what is
behind that upper horn, might want to have a luthier do it instead of trying it yourself; Guild always put a piece of stock behind the upper strap button. My Tacoma-build D55 had a nicely cut piece of stock, the NH F512 had a piece that must have been lying about the floor! NTL, it
was backed up so it did not fail, ripping itself out of the shell.