Those are called "exit blocks"..... You have not made any mention of where a line might be routed under the deck... that would be your first clue. Did the boat come with spinnaker gear? Maybe the spin sheets run to a block at the stern then under the deck to the exit blocks and out to the winch.... that's weird though... and totally unnecessary since the jibsheets will be out of the way if you're flying the spinnaker. The exit blocks are in a good position for spinnaker sheet "twings"... but I just can't imagine going to all that work when a simple deck mounted eye strap or padeye would be more than adequate. The aft cleats are not really positioned for an efficient tiller lock....but I've seen them on a few other V21's.... So there's obviously a common purpose.. keep looking at pictures... try "sailing texas" website. Good luck.