Well that's kinda what I meant D, 91', and #4 are all the same pheno.
I've agreed with almost everything you've said, but I have to correct one thing.
Chem D is definitely different than Chem '91. They came from the same bag of herb at the grateful dead show and the extra seeds from the person who sold Chem the herb sent out at a later point.
However, the first batch of beans he popped yielded multiple phenos. I've seen both plants from original cuts of D and '91 growing and I've seen the difference of Growth, taste, high, and sativa/indica profile between the two.
'91 is definitely the headie, sativa feeling chemdog. It is what was used in Sour Diesel, as well as OG Kush which is supposedly a 91 S1 - that tapped into some of the indica side of the chem genes from the self pollination process...
However, Chem D - is quite different. It grows more like an Indica, and the high is completely different. It has a straight indica stone, No speediness like the chem 91 - which has me buzzing in my head and body. The Chem D is a relaxing to the max indica stone with a nice head high.