The reason why people say Pre 98 is because that is when everybody started coming out with the feminized seeds and Bubba Kush was bastardized. Pre 98 Bubba Kush means original Kush, which will only be one bud. It is very apically dominant, you don’t get it to branch off.
It makes a very superior smoke, but you do not get much yield from it. That is why people will designate Pre 98/Post 98, because after Post 98, everybody played with it, mixed it back with the hash plant, and we started getting all this stuff that bred into all the crazy Kushes we have today.