For what it's worth, I use one pin on the forward thimbles and two for the rear entry thimble.
My thinking is, the front thimbles are short and tightly seated and if the pin hole is drilled thru the wood and thimble while they are clamped, they aren't going anywhere. Even if they did get a little loose, no one would notice it.
The rear thimble with the rearward extension could cause a problem with the extension raising out of the forearm if it ever became loose.
By using two thru pins in this thimble there is no way it could loosen up and rock back and forth.
Anyway, that's my theory. :grin: