Well, the point to remember is that "la banli nu pindi" refers to a particular something/someone that may not be a great depression. It's just a name. I could name my dog "la banli nu pindi", and then I could say "la banli nu pindi cu muvgau lo rebla be vo'a" But it would less likely to be true to say "le banli nu pindi cu muvgau lo rebla be vo'a" since here I am actually speaking about something that I am describing AS being a great depression (whether it is or not, that's how I'm choosing to describe it. It might be a dog, but that's highly unlikely). So if you are speaking about the period that in the United states lasted from 1929-1939, use "le" (or even "lo")
--gejyspa