Moldy Wine vs Dark Crimson

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Dark Crimson is noticeably darker, more saturated, warmer than Moldy Wine.

Can I use Dark Crimson instead of Moldy Wine?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Dark Crimson is noticeably darker, more saturated, warmer than Moldy Wine.

Can I use Moldy Wine instead of Dark Crimson?

The same difference applies the other way round: Moldy Wine is noticeably lighter, 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.