From my limited experience, Vass cordovans tend to fit 1/2 to a full size larger than their calf counterparts of identical size. I believe that David recently experienced this as well with his double-monks. YMMV.
The Vass shell cordovans definitely do run large and are variable in how large they run. Some for me fit fine right off the bat while others have needed an insole or a tongue pad and then fit well. Never any guarantees with handmade shoes unfortunately, but they do seem to hit the mark the large majority of the time thank goodness.