Looks like they must. I don't have a sidecar, just don't want to be that guy that put his on upside down if there's a standard way to set them by default
The sidecar mounting bolt position is determined by what sidecar and mounts are used. Bikes without a sidecar normally would not have a sidecar mounting bolt in the lugs or mounts that are welded to the frame. They would just have the frame mount with the unused empty hole.