Got back to work on this.  Have it bending to about 6" at 30#, tweaking the bends, about 2" to go before I'll string it...when I noticed that there's a spot where some of the fibers have popped loose on the opposite limb, not the same spot as the previous failure.  Man.
I think what I'm learning here is that hide glue doesn't adhere all that well to dogbane, compared to sinew.  It takes a ton of glue, and wrapping with string or ace bandage, to make sure it won't come loose.  Or just use diluted TB3, but I really want to keep it as primitive as possible.  (I used TB3 on the tip repair, so maybe it doesn't matter)
So.  I guess I'll reglue this section, wrap it, wait another couple weeks, and get back to work on it.  In the meantime, I have some nice, reflexed juniper pieces and a bunch of sinew lying around...