Do they all, though? Sure, the hardcore MLS fans do, and anyone who puts the time in will, but when you consider that football is still an up-and-coming sport in the US and that a large number of the new fans of this club are likely to be people who either never paid MLS any attention before or at least never made anything more than a mild connection - especially the young kids NYCFC will want to reach out to - are they really all aware? I mean, I've seen plenty of people on social media ask rookie questions about NYCFC, such as not knowing about the Yankee Stadium deal. I periodically look at #nycfc and for months after the team's announcement I saw new tweets saying "wait, there's a new team in NYC now?" I know for sure that there are still a lot of MCFC fans over here who have never heard of NYCFC. I reckon that if you were to sample the NYCFC fanbase of 5 years' time, at least half of them wouldn't know of the CFG connection right now.
Of course, I'm not US-based, so I'm going off instinct and intuition, but I reckon I'm not far wrong. Also, don't mistake this post for me saying that I am arguing for a stronger link to CFG. Obviously I'd be happy for one but I'll accept it either way. I just think you're shooting wide of the mark by claiming that everyone knows there is a connection between MCFC and NYCFC.