you are confusing two completely seperate laws:
1) One law says that a person can posess a maximum of two wild caught California native rosy boas (so this law doesn't apply to rosys that are not indiginous to California, like Mexican rosys)
2) Another law says that a person must have a fishing license to hunt for rosy boas, and the catch limit is two.
Just resist the urge to think of these laws as related to each other. You don't have to "prove" that the rosies you have were caught while you had a license. Similarly, you don't have to prove that tha car in your garage wasn't speeding yesterday. If you didn't get a ticket yesterday ( or didn't speed) then it's over.
The only "proof" one would need concerning rosys in possession is paperwork (receipts) to prove that any rosys they have, IN EXCESS OF THE WILD CAUGHT LIMIT OF TWO, were purchased from a breeder. So if you had three rosies in your possession, and you have a receipt showing that one of them was purchased from a breeder (with a permit), you are legal.