ΔE 13.6, fair: the same colour family, but not a straight swap. Coven Purple is a little darker, more saturated, cooler than Violet. They are different kinds of paint: AMMO by Mig Violet is an ink, glaze or transparent paint and Army Painter Coven Purple is an opaque base/layer paint, 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 14). Coven Purple is a little darker, more saturated, cooler than Violet. They are different kinds of paint.
The same difference applies the other way round: Violet is a little lighter, more muted, warmer.
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 Violet on the colour wheel See Coven Purple on the colour wheel
All matches: Violet equivalents · Coven Purple equivalents