Using documented recorded sources to identify the form known as the "blues" is one way to do it. Another way is to show the musical influence from early blues forms and how they were used by New Orleans jazz musicians and chanteuses such as Bessie Smith, Ma Rainey and others. These morphed into the early jazz and would be absent in this style were it not for an acknowledgement of earlier forms of the blues. I would argue that branding in a style of music is often rigid and that music flows in variation and form through earlier influences of its practitioners. For example, one of the finest blues musicians who ever lived was Charlie "Yardbird" Parker who took the blues to a advanced musical art form. Blues scales morphed into be bop scales. Much of what we know of this music emanated from modal scales of West Africa and were transported over here during slavery. Here we see a dichotomy of approach, academic versus artistic, the former formalizing in a rigid pattern, the latter a growing, developing musical cell resulting in new forms and constantly changing.