He may have thought "Otca" meant "model A", because at one time the theory was that "OTCA" stood for "Old Town Canoe [model] A".
Old Town discontinued the grades in the '50s, and build records of this era onward contain less information. The canoe may have had spruce inwales and mahogany outwales... someone else may chime in with a more definitive answer, based on canoes that they've worked on.
Kathy