ΔE 11.8, fair: the same colour family, but not a straight swap. Corvus Black is a little lighter than Grim Brown.
Can I use Corvus Black instead of Grim Brown?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Corvus Black is a little lighter than Grim Brown.
Can I use Grim Brown instead of Corvus Black?
The same difference applies the other way round: Grim Brown is a little 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.