ECSD is clone only and SD can be found in seed form.
Sour Diesel IBL was based off of the original ECSD clone only. SD IBL is pretty much ECSD in seed form.
The term East Coast Sour Diesel was coined by Rezdog back in the days of OverGrow.
At that time the original Sour Diesel clone was making its way across the country and Rez thought that the SD clone floating around Cali/left coast was different than the original so he termed the phrase ECSD(of course it was all the same clone).
Now that Rez has developed a seed line of SD most people have started calling the original clone ECSD and refer to his work as sour diesel.
Old timers who have had the clone as long as Rez still call it by its original name, Sour Diesel.
Soma's NYCD is Sour Diesel x Hawaiian Afghan.