I have experience with epileptic pups as my youngest has had seizures since he was 1 1/2 years old. The first time he had a seizure the vet put him on medications after he had 3 within a few days. Now, he is on several meds and CBD oil and a special neurocare food. He was maxed out on meds, and I wasn't seeing an improvement, but I have seen a dramatic improvement since CBD oil was started.
With your pup, I would be concerned that if he does have epilepsy it has never been controlled by meds. If they have ruled out any poison and his bloodwork is fine, I would get a thyroid test as well. Mine had one and it was normal, but it was something that the vet said could be the cause. It just wasn't the case with mine. Another option would be an MRI, which was suggested to me when Yukons seizures kept getting worse, however I opted against it because it would put him under more stress and regardless of the results I would not change his treatment.
I would just talk more with the vet and see what they think about putting him on meds to control them.