You are correct - 12 O.C. - is 12 inches on center for your spacing schedule and anchors. Assuming the front of your shed will include the door placement - this is why the design loads require more anchors. Wind loads for an entry door located in a wall structure may require stronger connections - more of them. You may see maximum design pressure ratings for opening in the walls 'zones'. The (psf) maximum design wind load can also increase depending on the location of the door (or window) if near the corner of the building as opposed to a placement in the middle of the building.
Hurricane Preparedness Expert.