Sure they had a couple of dance club hits, but that doesn't make Yaz a disco band. While one of my favorite new bands in their day, they only lasted a couple of albums and were never kings of anything. If we want to pigeonhole them to a genre label, wouldn't it be New Wave? With lineage from Depeche Mode to Yaz to Erasure and Alison Moyet's solo stuff, I think of all of those as New Wave and none as disco music. Cheers,
Spencer