If your intent is to do authors by series, I believe the way to manage that would be to have collections marked by series.
For example - Joan Hess has two series, Claire Malloy mysteries and those set in the town of "Maggody", so there'd be one called "Hess_Maggody" and the other "Hess_Malloy".
What exactly are you hoping to accomplish with sub-folders?
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