Middle thwarts were optional on some Old Town Canoes. The 1920 catalog page at http://www.wcha.org/catalogs/old-town/specific.gif includes the statement that middle thwarts would be "furnished without extra charage if specified when the order is placed." This page in the 1950 catalog states "No middle thwart in 16 foot canoes but furnished with extra charge ($2.00) if specified when order is placed." This is why middle thwarts were only occasionally mentioned on the build records and resulting database but appear much more frequently in the actual canoes.