Thanks to @Craigson15 for the quote. There’s a little bit more to it. As I understand it, the original chem cuts are:
Chem 1 (sativa-ish)
Chem 3 (very fruity and citrusy, regarded by many as the best of the chems, but super rare and hard to dial in. Still held by bodhi and nspecta and one of the admins at Breedbay - mom to the triple HT cup winner Sunshine 3 accidentally renamed Sunshine 4. Also used in bodhi’s Cobra Lips freebie that was available for years)
Chem 4 (biggest yield of the bunch, but not regarded as potent as the 3, the 91skva, or the D. I don’t know anybody who considers it the best cut, but what do I know? Not much. 
)
Chem D (as mentioned in the OP, known for extreme potency and smelling terribly wonderful, body odor, garlic, bad breath. Also pretty unstable itself, but usually good when crossed to stable males.)
Chem 91 Skva (shared with SkunkVA by Chemdog and kept around all these years. Looks like an OG in some ways, very potent, the most potent cut for some, but finicky and throws nanners a lot).
Chem Sis (I don’t know anything about this one)
These are the cuts that came from the original ounces of “Dog bud” that was shipped to Chemdog in the mail by the people who sold him his first sack of it at a dead show in 1991.
Love him or hate him, but Adam Dunn got all of the Chem crew together in one podcast a few years back. Literally all of the folks involved in the original dead show sales, seed popping, cut saving and origins of diesel. I took notes as I listened to the show. Here are my notes:
Pbud starts telling the story, then they call chemdog “G” himself and he tells the whole story, then they call AJ “Asshole” the Sour Diesel guy, and finally they call Swerve.
Forgive the shitty video - the audio is what you need to listen closely to.
Some highlights:
In 1989-1990, Joe Brand, Pbud and the Crested Butte, CO, deadheads were getting something called Dogbud from what they were told was the Cali/Oregon border. Dank, skunky, and indoor.
They called it Dogbud because after you smoked it, it made you roll around on the floor like a dog. They thought it had to have been grown with chemicals because it looked amazing, but also because it smelled and tasted like chemicals. “G” and JB put the two names together to come up with Chemdog. The DAWG name likely came from Brett at Apothecary Seeds when he had bred some beans from the Chem 91 stock.
They sold a pound of it at the Deer Creek Dead show in 1991. Chemdog bought a bag, then came back for a zip and hung out with them at the show, exchanged numbers. Chemdog got in touch with pbud, and bought a couple/few zips in the mail. One of the zips had 13 seeds in it, but they never found any other seeds.
Chemdog sprouted the first two seeds that year - 1 male (discarded - D’oh), Chem 91 Skunk VA. Then he popped a couple more beans, Chem’s Sis came from that 2nd round of popped. In 2000-2001ish, he germed 4 more. Chem D was the keeper from that round of popping. They see only minor variances, so they think these original chem seeds might be “selfed.”
The original Chem 91 Skunk VA is the same cut as the original New York City Diesel (originally called Diesel). In the early 2000s, Joe Brand called Pbud and mentioned the NYCD. People were getting clones from Massachusetts and changing the name in NYC.
The “Sour” name came from Staten Island, they speculate that perhaps it’s a cross of Chem 91 Skunk VA with Mass Super Skunk, or a herm from a separate cut in the same room as the Chem 91 SKVA that ended up being a nice cut.
In 1993, Chemdog met AJ on a deadhead tour bus, and Chem said “check out this Chem 91” and then AJ said “check out this Sour Diesel” and they realized they had the exact same cut.
I ended at https://youtu.be/uCrvpTcEWPY?t=5428 before they spoke to Swerve.
The Chem 91 JB cut is not original. It was held by Joe Brand, and was originally thought to be the Skva cut and even was verified as that cut by Chemdog at one point, but is different. Produces more knobby buds and more colas than the Skva cut. Unsure of where it comes from, but could be a chem91skva s1?)
@newb2.0 the Chem 91 skva s1 from CSI are known for being very very very unstable, as far as I’ve read. Probably better in crosses or trying to get the cut itself.