Skilled craftsmen trained in the designs and techniques of the pre-WWII ateliers were still around in the 1950s and 60s, and were producing good quality work prior to the start of the Cultural Revolution in 1966.

While Hong Kong likely served as an outlet for foreign purchasers denied entry to Beijing, after the US embargo ended in the early 1970s demand seems to have encouraged the Beijing Enamel Company and its ancillary workshops to streamline designs and production to accommodate an expanded workforce of less skilled workers. Hence the stereotyped floral designs replacing the more elaborate and individual designs from the earlier decades. One of the old cloisonne masters described how Hong Kong buyers used to camp out in the hotels surrounding the factory, eager to buy. And you yourself witnessed what was available in Hong Kong during the Vietnam war years, with US buyers flocking there to stock up because chinoiserie was once again all the rage.

http://www.beadiste.com/2016/01/puzzling-evidence-evolution-of-fish.html

http://www.beadiste.com/2015/02/puzzling-evidence-beijing-enamel.html

http://www.beadiste.com/2013/11/puzzling-evidence-jingfa-cloud.html