I think that many of the more modern coatings are flourides, and are used by the manufacturers for abrasion resistance as well as their optical characteristics.
I do know that I have the front element of an Olympus OM series zoom lens that crashed off the car roof, which I use as a magnifying glass and "clean" with the tail of my shirt with very little worry about the cleaning.
I've been doing this for well over 10 years and the lens is still "Like New" as to the clarity of the glass.
So, I'd say the coating is pretty tough. I've never seen mould on a lens made later than the '60s, but my old Leica & Canon rangefinder lenses did get some mould when I lived in humid Maryland.
Hopefully someone with more specific knowledge will respond.
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