I had a male cat with cystitis in 1985. I was only 24 at the time but I knew what was wrong when he jumped up on the table and peed in front of me because I had a cat care book that I read all the time. I took him right to the vet (had to take a taxi, I didn't drive in those days) and he was found to have no infection, just inflammation. The vet diagnosed cystitis and told me to feed canned food only, and no fish.
So even back then there were vets who knew this. That was when I started feeding a canned food diet to my cats, (no fish) the two I had then and every cat who came after. Until my FLUTD kitty, that is. She was eating a canned diet when her crystals started. The c/d is the only food that keeps the crystals at bay, and she won't eat the canned c/d.
Incidentally, that day I took Baby to the vet in the taxi, I had to walk home because I had no money left for a cab. Lugging a 13 pound cat in a carrier 7 miles was a labor of love, LOL.