Can any joint size be blown onto any size piece? (i.e. a 19mm joint on a mini rig, or a 10mm joint on a 2ft waterpipe)

Yes, the joint size is usually chosen by the blower for the size of the rig.  A 19mm female would look crazy on a 3 inch tall dab rig.  We find the 14mm to be the best overall size for the industry.  Not too big, not too small.