ΔE 11.9, fair: the same colour family, but not a straight swap. Astorath Red is noticeably darker than Dead Red.
Can I use Astorath Red instead of Dead Red?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Astorath Red is noticeably darker than Dead Red.
Can I use Dead Red instead of Astorath Red?
The same difference applies the other way round: Dead Red 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.