Yes, welcome Dan. Glad to see someone from PTF here. How's the Abyssinian coming along?
Speaking of "board roofs," that really is a fascinating thing to ponder. Never heard of them before. But makes sense that they'd have been used on the out buildings of poor homesteaders. Not sure I buy them being used in town on homes, but there is much we don't know about history.
Shiplap does make sense, as does tongue & groove, board & batten, etc. What might be most problematic would be hiding/covering nails as exposed nails will always leak water.
Tongue & groove allows "blind nailing"...but exposed boards would move and shrink in the weather considerably...must have been a loosing battle. I thought early roofs in the "New World" were often thatched.
Would be interesting to see if anyone could find and post a reference to plain old "board roofs"