No hidden damage tricks on those dark scars from previous hunts, just takes more work to reopen them. You'll see white marks first then red wounds that actually give damage boosts when you hit them, those are what you want to focus on. Fresh wounds glow nice and red in focus mode, perfect for landing those focus strikes which really mess monsters up and leave the dark scars behind. Pretty much means you're better off making new wounds than trying to reopen old ones, especially on those nasty tempered variants that show up with permanent blue scars.

When you get a fresh wound going, that's your moment - smack it with focus strikes for some sweet weapon buffs and maybe knock the monster down if you time it right. Other hunters can jump in on the same wound too, getting those hits in before it turns to scar tissue. Tip you might find interesting: if you're playing multiplayer coordinate with your team to focus the same spots, way more efficient than everyone hitting different areas.