|Image from Urban Decay|
So I am sharing the resulting table with you.
On the row, you'll find the palettes, on the column you'll find the single shades of eyeshadow. You'll notice that UD has been really careful to put in each palette only one or two eyeshadows from other palette.
As a result, I own 2 Foxy shades, 2 Half Baked shadows, and 2 Blackouts; I also know now that I own half of the new Dangerous palette thanks to me having the 15th Anniversary palette.
It's quite handy. So without further ado, here the link to the table
Most of the single pan eyeshadow are in one or more palettes, so think carefully and check the "cheat sheet" to see if you don't own the shade you want already or if purchasing another palette may be cheaper.
The table (cheat sheet) is currently on Google Docs and I'll work to keep it updated and I'll try to make it easier to read.
Hope it helps!