ΔE 14.4, fair: the same colour family, but not a straight swap. Permanent Violet Dark is more saturated, warmer than Medium Violet.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Permanent Violet Dark is more saturated, warmer than Medium Violet.
The same difference applies the other way round: Medium Violet is more muted, cooler.
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 Medium Violet on the colour wheel See Permanent Violet Dark on the colour wheel
All matches: Medium Violet equivalents · Permanent Violet Dark equivalents