Also one of the telescopes on Mauna Kea, Subaru I think, used silver. They vacuum deposit it and overrcoat it as I recall. A small minority for sure.
I checked on this - one of my clients works there and does coating, among other things. He said they did not do any overcoating, just bare aluminum for the primary mirror, optical secondary and tertiary, and bare silver for the infrared secondary and tertiary mirror.
Also the symptomology is wrong, the defects are more likely what I posted in 2016 in that thread - contamination of some sort.
I agree, this is not an "enhanced" coating issue, this is an issue caused by contamination of the chamber or faulty stripping of the previous coating.