I've never seen that j mold material on any houses around here. Stucco houses here were mostly built in the early 1900's to the '50s. The stucco would be applied right up to the doors and windows.There is a metal J mold that goes around every window and door as part of the lath. It provides a surface to screed to. It does not bend for round windows.
Metal lath is an open mesh material that will conform to curves.