I believe that is normally the case, but this wouldn't be the first time a particle was discovered before being predicted. The muon was discovered before an ac

I believe that is normally the case, but this wouldn't be the first time a particle was discovered before being predicted. The muon was discovered before an accurate prediction for it was made. There were some known gaps that people tried to fill with particles related to muons, but no one quite predicted that there was a particle identical to an electron but with a larger mass. The tau neutrino was discovered without any prior reason to believe it existed. We knew of neutrinos and they seemed to fill the only related gaps we had. It wasn't until the tau neutrino was experimentally detected that we even realized there was a gap for it.