More Mortising (Continued from Oak Chair Post)

Looks like this chair could be pretty old too. I was able to get the seat off, and to a loose joint that I could peek at. Looks like hand cut notching to me. I believe these types of joints are called stub mortises. It is a shallow mortise that does not go all the way through.

Photo 1 & 4: The same loose joint, looks like the tenon broke at the top.

Photo 2 & 3: Joinery at the bottom stretcher. Looks like the same type of method was used.

Any thoughts?