I might be totally wrong, and you can call me an idiot if I am. But from what I can remember, they stocked pure Florida's in the early 80's and that's when the lakes (Fork in particular) started taking off. Then they started the SAL program in like 85 or 86 to keep track of the genetics. I am not sure how long they stocked pure Florida's but I would think they would all be F1's at this point.
Like I said, I could be wrong, but this would be my opinion.
I would imagine that's why they take a swab of all the fish over 7lbs caught in the BPT events, to see if they are F1's.