Karl, I believe the transistion from scribe to square rule layout was accomplished without new tools, rather a different protocol. The great motive for change was the abundant work opportunities that came with rapid westward expansion, the carpenters that could adapt would complete more work and prosper. When we modern folk think of scribe rule, we tend to think more about the technique of joining piece to piece and less about the overall layout and control of the building. If we look at building control, from the step and tally method, then we may see much more similarity of method between square and scribe rule.
I would like everybody reading this thread to add something. The topic is not closed to early square rule, rather the general topic is adaptation. I hope we all do adapt.