We had the same situation come up. We paid off our tractor last June. Got to wondering about a paid-in-full letter not arriving. Finally in late September the papers came in with a thank note. Apparently they just don't get in any hurry.
Trying again for those in need.
http://kubotabooks.com/AutoIndex/index.php?dir=Tractor%20Owners%20Manuals/&file=L3301%2C%20L3901%2C%20L4701%20Workshop%20manual..pdf