Pretty sure I am on the same page as you guys but just don't understand how tying knots in the main sheet will keep the line from bring pulled through the actual front cleat when pulling from the rear. I'll take a couple of pictures of the issue once I get home this afternoon.
You do realise that the mainsheet is one very long piece, don't you? So without knots at each end, if you pull the back end, the rope will pull (forwards) through the front cleat, through the turning block on the right side in front of the front crossbar, through the fasirlead midships on the right of the hull, through the turning block on the right side of the rear of the hull, through the block attached to the deck behind the rear 8 inch hatch, through the block attached to the rear of the saili, back through the rear deck block, through the second turning block on the right side on the rear of the hull, forward through the turning block midships on the right of the hull, and up through the cleat on the rear crossbar. At this point, you will have removed the blck mainsheet from your TI.
So the knot at either end prevents you unravelling the mainsheet. Does this help?