... interesting question, Arthur.
i have no answer at all, after reading your question, i went to browse any info available out there, unfortunately nobody mentioned to link JLC watch to GG, only those commonly known watches are UG, Omega, IWC, and PP.
my best guess is at those years of 70s, watches with the shape like this are very popular and high demand, it is likely watch companies to design similar shape or even copy the design
in any case, your question has added some interesting side-story to my watch, i keep it in mind and try to find out more along this line. thanks!
by the way, happy to hear you are getting into vintage watch world, we can share more common interest
stefan