I don't.
Yep I've ended up with duplicates which occasionally turns out handy, but I've bought scads of paints which are supposed to live in a cabinet draw, but spend 99% of their time on the painting table.
90% of my paints are VMC which I've gradually bought over the last 8-10 years and it's most of the range.
Of course my painting room has a unique filing system called IITS! (It's In There Somewhere)
Have too agree, not the same amount of paints but they are sorted in one big pile in a box... just look and pic what I need... no clue what are in there or not.
On the other hand I do write down what colours i used for which part on a figure, atleast most of the time.
Figure xxx cape
base light blue
shading 1 little dark blue added to light blue 2 parts water
Shadin 2 More darkblue added 3 parts water
Shadow glaze some dark purple glase and cold blur black colour 6 parts water
Higlight lighter blue
higliht glaze warm colour xxx if needed in some areas...
And so on, that gives me some control that if I want to recreate something I have a general idea how I should do it.
what to buy in the future, that is more of I am in a shop and that colour looked nice, or that I want to try...