All of the older trad recurves and longbows were made to be shot “off of the hand” or “off of the knuckle.” There was no “shelf” to shoot off of. Then some enterprising bowyers started including a little built up section at the top of the grip wrapping. This could be something as simple as a little wedge of wood wrapped in place forming a small ledge that could help hold the arrow in place. Soon these bows also included an insert of a harder wood or other material to prevent wear from the arrow sliding against the bow.
Since these little ledges held the promise of better accuracy they grew in size until a substantial arrow shelf was built into a built up handle section. And as sights become popular the little cutout grew to facilitate being able to see your sight and the sight window was born. (Also, “centershot bows” allowed arrows to be aimed and shot closer to the central plane of the bow.)
So, to determine if a bow was designed to be “shot off of the arrow shelf, there has to be a substantial shelf built into the bow (at least the width of your arrows) and the shelf has to have a hump built into it. If the arrow shelf of your bow is flat, it was built to be shot off of an elevated arrow rest (which often were of the “stick on” variety which can and did fall off and get lost even in storage). The crown or hump on the arrow shelf was there so the arrow touched only a small area of the shelf meaning less friction and less possibility of a “clearance problem.”
The shelf and the side of the bow adjacent to us was often covered with leather, to prevent wear on bow and arrows and also to provide a bit of “give” to help the flexing arrow on its way, much as cushion plungers now provide.
When the shelves became very large, a way of “adjusting” the centershot of the bow was to build out the side of the bow with multiple layers of leather or whatnot. This was called the “build out” and you can read accounts from back in the day of archers setting their “build outs.” Now you know what they were doing.
Photos below show the crown of the shelf of a bow designed to be shot off of the shelf, the leather pads used there, and how different shooting off of your knuckle was from shooting off of a shelf.