ΔE 15.9, loose: different enough that you should pick on purpose. Navy Blue is much more saturated than Night Lords Blue.
Can I use Navy Blue instead of Night Lords Blue?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Navy Blue is much more saturated than Night Lords Blue.
Can I use Night Lords Blue instead of Navy Blue?
The same difference applies the other way round: Night Lords Blue is much more muted.
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.