I never converted (that is, I used digital from the start), but I have organised my sheet music in folders and subfolders: Classical, First half 20th century, Contemporary, Pop, Film, Collections. Within each folder, there are sub-folders, for instance Classical starts with Attwood, Bach JCF, Bach JS, Bach-Busoni, Beethoven etc. Then within those folders, there can be even more folders, for instance Bach JS has Bach Inventions, Bach Notenbuch, Bach Preludes.
I am truly pleased with my system.
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... feeling like the pianist on the Titanic ...