NYC Chem F2 = Chem D X 91 Chem BX
I found this comment by DankFrank on icmag about this F2 that made me interested in this one
ONYCD = Chem '91 x Tres Dawg
Tres Dawg = Chem D x Double Dawg - Chem D Bx2
Double Dawg = Chem D x (Chem D x Afghani#1) - Chem D Bx1
Chem 91, Chem D, Chem 4, ECSD - are all related. The Chem 91 being the original parent.
So, without using JJNYC's naming schemes - Chem D x (Chem '91 x Chem D Bx2)
What you have is a very serious chem line breeding project that should give you some fairly consistent type plants, even when F2'ed theoretically.
You'll find 9-10wk plants that will stretch about 2.5 times once flipped in flower. The '91 is a more sativa type plant in behavior. Has elongated internodes and chunky flowers that don't exactly make long colas. However, Chem D is a good yielding plant and produces some fat buds when grown right. Is more compact than the '91. Some of the best resin for extracts there is. True FMCD bubble. Essentially, you're going to find all around hybrid type plants that sit very middle of the ground. Outliers will finish 8wk or 11wk respectively. Keep in mind JJNYC used Afghani for the original chem outcross and NO ONE really knows what the genetics of Chem '91 are. It's fair to assume, it's a sativa leaning hybrid of some type. (think 60/40) If you find longer flowering plants, you know you are seeing something that is more heritage and relatively unknown.
I'd be looking for a garlicy, old gym sock, earthy/musty, damp basement smelling skunk, that has a sharp, bleachy smelling stem rub. The '91 should have added back some more subtle sour and lemony type notes absent in the Chem D.