there were a half-dozen people that i sent preview images of GND4 to throughout her development;  i will definitely play my cards closer to my chest from now until a product's release

Steam engine time.  Figure of speech derived from the fact that the steam engine seemed to appear from several different people in widely separate locations at the same time.  Also seem in the development of calculus, and the airplane (the Wright's just barely made it as first).

It happens.

I still believe that there are too many similarities - to both GND2 and GND4. if it truly is a coincidence and the similarities are unintentional, then whoever made it (or it was contracted out to) should have picked up on them and tweaked it to be more original

Why?  Assuming it was coincidental, and no foul play involved by all parties, if creators of any form had to change gears just because someone came out with something similar, nothing would ever get produced.

Writers have long used the mantra that there are no original stories to get over the fact that sometimes they'll produce something that unintentionally looks like something else, or that two similar works will come out at the same time.  Apparently visual artists haven't come to that realization yet.