I would say that it takes four generations, rather than four years to stabilize a new strain. But again, I'd like to second what everybody else just said.
Getting seed stock from the original breeders is the only way to be really sure what you're getting, but there a lot of great F2's and hybrids done by other breeders than the one that did the original strain.
I'm really not sure about Nirvana and where all their NL genetics come from, but I have heard that the original NL5 was a NL with a slight Thai sativa influence bred into it 4 or more generations back. It's hard to know for sure, there's no licensing of new cannabis genetics, and I don't know when that'll be arranged!
-the man with the golden nug |