Ken,
Perhaps my statement was over-reaching, but I am not yet convinced.
Has it has been verified that the peg holes you are referring to are not drawbored? If so, that is very interesting indeed, and raises quite a few thoughts about how they managed to pull the joints up tight enough to drill through them. Spanish windlasses? Drill them in situ after gravity has brought the joints home tight?
I feel compelled to mention that we have quite often and with no ill effects draw-bored centered tenons on posts as wide as 12". In fact, there are about 200 draw-bored pegs which pass through centered tenons on the frame we are assembling now. (These are all 2" tenons centered in 10" posts). I don't know of any reason why it wouldn't work unless your peg was too fat on the driven end to go into the hole deep enough (easily remedied) or your hole isn't deep enough to allow the peg to pass through the tenon enough to draw the joint up fully or your peg was too short.
I have wondered if the tendency to offset tenons/mortices to one side is so that the peg holes won't have to be drilled as deeply in order to drive them to the point that the joint is drawn up fully. I know that I have seen pegholes that were not drilled through in quite a few old frames. Having the tenon shifted over as far as possible keeps the required peg hole depth to a minimum and it keeps the required peg length shorter. Double time saver.
Gabel
