Since you can use all 16 characters on an SD Card, I use folders to indicate either origin or style. For example songs which I downloaded from the KESO site are stored in folders like Banfield_1, Banfield_2, etc. Or when it is about styles I call the Ballad_1, Ballad_2, Jazz_1, etc.
And with SD-Explorer I can easily shuffle and move songs from one folder to another.

Nevertheless I have not yet found the right system. I mean I have not added info about the SD Card. The idea of mentioning the size is nice, but irrelevant to me. I am thinking of writing numbers on the SD-Cards and then add this number to the folders and songs. But I did't get to it yet.