A Reader Question Re: Deep Groove, Flat Edge

Sorry I haven’t posted in a couple of days. Was stuck in a snowstorm without my computer. It was like being cut off from civilization. Anyway, I’m back and will soon get caught up on all I’ve missed in the Jazz Collector world. In the meantime, one of our readers posts a question for our readers: What is the derivation of the deep groove and the flat edge? Where they technical considerations that were later abandoned as the technology shifted? Were they specific to certain labels and pressing factories? It’s a good question and I’m sure searching deep on Google may provide an answer, but perhaps we can provide a shortcut and fodder for interesting conversation by asking it here. So, to all, whither the deep groove and the flat edge?