What, really? When I met him in 2015 he was introduced to me as a brown belt (it was no-gi). Did he really go from blue to brown in less than a year? I didn't know that.
Also, as far as whether Cummings taught leglocks to the other top Renzo guys:
Some of them his influence is pretty clear. Some of them do it in a very different way. Eddie's influence is much more obvious on Jon Calestine, for instance. If you've seen Eddie's new leg lock videos and how he uses his thighs for breaking you know what I mean. That's how I've been doing it for a while now (though not nearly as good) but I teach my longer-legged students to do it more like how Danaher shows and Gordon Ryan does it.
I do think that Cummings is responsible for a significant fraction, perhaps even a majority, of the leg system as it exists and is taught there.