ΔE 21.0, loose: different enough that you should pick on purpose. Amulet Purple is noticeably darker than Violet Coven.
✓ Two Thin Coats comparison chart lists these two as equivalents.
Can I use Amulet Purple instead of Violet Coven?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Amulet Purple is noticeably darker than Violet Coven.
Can I use Violet Coven instead of Amulet Purple?
The same difference applies the other way round: Violet Coven is noticeably lighter.
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.