1) does the frame has a fixed derailer hanger, or is the hanger clamped under the acorn nut of the q/r?
Clamped hangers usually come with a screw and a funny looking nut that fits in the dropout slot to keep the derailer in place when the wheel is removed. That tends to eat up 1/3" or so of driveside slot.
2) with horizontal dropouts, the length of the chainstays and dropout insertion doesn't have to be spot on. As a consequence, it may well not be.
Although rarely as offset as yours.
3) If it works, it works. Ride more, fret less