You're right Kushes weren't usually advertised as Kushes. Most folks simply referred to them as Afghani, Pakistani, or Mazari, but weed nerds and breeders did call plants from the Kush region Kushes long before 2000, I think that Hindu Kush was definitely advertised as such earlier than 2000.
OG Kush has very little true kush genetics in it, but it was so good that despite that fact people still referred to it as Kush because the term Kush had already been popularized as being a term for good pot before OG was a thing.
I grew up in a growing region so most people didn't buy from seed catalogs, people just traded strains and didn't bother with names. The name "Kush", or "Skunk" was used a lot back then. Like, "Oh that's that really good Skunk weed that Billy Bob over the hill grows". Not that I had anything to do with it, but, that's kinda similar to how OG got named, it grew with the characteristics of a Kush type plant, so they called it a Kush.
The advantage of growing up in a growing region is that I didn't have to run the legal risks of ordering through a seed catalog, the disadvantage is that I never knew the names of many of the strains that I feel nostalgia for now, or they were strains that were never available in seed catalogs to begin with.
I first grew a cut of Jack Herer in probably 2006, a little late to the game, but it was fantastic.
