Gabel, TImberwrestler,

thanks for coming on with your observations. I was aware of the use of 'L' posts in the east, but until now had never been able to completely confirm this practice locally. Like you said, they are almost all behind plaster or paneling, it's very rare that we get to see one of these. Most people that have them, don't like them, because the way they were enclosed makes them dirty, drafty, uncomfortable homes.

Take a closer look at those braces, many are in fact housed. On some ,the dimensions on the timbers were close enough that no housing was necessary. In fact, the dimensional precision of the primary framing members is extremely high, even though the finish is very rough. Only studs are imprecise, this in the dimension that they did not need to be precise.
I'll have to go back to this frame and study it more closely, to get evidence needed to determine exactly what is going on.

Part of my opinion of layout does stem from who it was that built this, most likely Amish carpenters who were a part of the first group of Amish to come to this area. The important thing we have to observe about this group is that many of them were immigrants or the children of immigrants who had come from either Switzerland or Alsace, and have been shown elsewhere to have carried their Old World practices with them (for example, study closely the framing method of the floor and of the roof on this structure)
Center line rule -a means of shortcuting full scribe, in the same spirit of edge square rule- is a practice of their homeland from that period, and is a practice I have observed in use in Swiss style (short studded, long braced) frames in Adams County Indiana. It wouldn't surprise me to see it here too.

But if this is in fact the case, we shouldn't look at it as part of the lineage of classic square rule, it's another very similar tradition.

This is a method I have seen used in barns and roof framing in Switzerland, the only difference when applied to a house frame is that generally the entire timber would be carefully conformed to the lines established from a central reference, not just the joints. But on this American frame, where the frame itself was immediately buried under siding and plaster, this would have been totally unnecessary.