ΔE 13.4, fair: the same colour family, but not a straight swap. Ancient Copper is much more saturated than Iridescent Copper Light (Coarse). They are different kinds of paint: Golden Iridescent Copper Light (Coarse) is a pearl paint and Vallejo Ancient Copper is a metallic, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Ancient Copper is much more saturated than Iridescent Copper Light (Coarse). They are different kinds of paint.
The same difference applies the other way round: Iridescent Copper Light (Coarse) is much more muted.
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 Iridescent Copper Light (Coarse) on the colour wheel See Ancient Copper on the colour wheel
All matches: Iridescent Copper Light (Coarse) equivalents · Ancient Copper equivalents