By contrast, there's no way to confuse Marisa with Patchouli, or Murasa with Nitori, or most any of the others.
I assure you that, if you're me, it is astonishingly easy to confuse them! :D
Only way I recognise Patchy is from her hat. I can only tell Remilia and Flandre apart if I can see their wings. Whereas I have no problem recognizing Nagato or Mutsu (or Tenryuu or Tatsuta or Hibiki or...) even if they're drawn in street clothes different from their shipgear or their usual outfits.
It's a little frustrating, really. Obviously there is a wealth of excellent Touhou Project material out there, and I wish it didn't bounce so hard off of my brain. Apparently when it comes to Touhou Project, I am unfortunately like Jack Burton: I was not put on this earth to "get it".
(I keep trying, though! If nothing else, I can still enjoy Mokou x Kaguya.)