Wilgus's invention of the term "blues ballad" was a misnomer and is not useful. The ballads that were not blues songs and were around long before people began talking about "blues songs" were bad man ballads, often had 12 bars, and does that mean we should call them "blues ballads," no. We don't call Sam Cooke a "disco soul" singer just because he was a soul singer and soul influenced disco.