ΔE 16.4, loose: different enough that you should pick on purpose. Iridescent Copper Light (Coarse) is noticeably lighter than True Copper. They are different kinds of paint: Army Painter True Copper is a metallic and Golden Iridescent Copper Light (Coarse) is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Iridescent Copper Light (Coarse) is noticeably lighter than True Copper. They are different kinds of paint.
The same difference applies the other way round: True Copper is noticeably darker.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See True Copper on the colour wheel See Iridescent Copper Light (Coarse) on the colour wheel
All matches: True Copper equivalents · Iridescent Copper Light (Coarse) equivalents