I sure enjoy the comraderie between you guys, and Don no offense on "the older generation thing" I am older and proud of it in lots of ways!
I always knew the lower sills to be called mud sills the term was picked up from my father's generation of craftsmen, and just carried forward.
We also used a false tenon guage for the mortise holes that fit exactly the tenon guage in the photo. If you used both of them as you created the various mortises and tenons, you could be fairly sure that everything was going to fit providing all other criteria was met, such as squareness, and the timbers being in plane.
We had a discussion a while back on seatings on the upper sides of the mud sills, you can see we have prepared the locations of the vertical posts of the upperframework as you look in the background at some of the other timbers lying around in the preparation area.
Some of the longer timbers were 36 feet in length (the barn being 3- 12 foot bays), and these timbers in the rough were about 38 feet long to allow for trimming and squaring the ends.
I believe you can see one of these adjacent to the foreground timber.