Sandy, when I bought a Canham 5x7 wood camera, around 1997 I wondered the same thing. I think Keith told me that many people were using his cameras with a Technica adapter, for Technica lens boards, rather than his Toyo standard. Technica boards do not center the lens on the board (I think it's lower than center) therefore, he didn't want to make a standard detent. I think you're right though. I ended up making pencil marks on the standard for quicker setup.
Take care,
Tom