Thanks sharpshooter,
This certainly explains some of what all of us experience while playing "musical barrels"!

Question: Does "slipping the joint" physically displace or deform the threads themselves, in order to hold the new alignment? Or does it just reposition the barrel on the threads as gravity does on loose threads?

If it is just repositioning, then a properly fitting fixture (A good stock) could be used to set barrel straight before torquing.