yeah, if no spread, no worries. picture 8 of 10 does look like a necrotic spot, though. harder to tell with that lighting, you'd know better in real life. picture ten looks like you could rub it off, and if dusty more likely nutrients that water dried up and left. again, if it doens't grow, it's not microbial. try gently rubbing it upp without damaging any tissue, otherwise leave it.