Retro, the discussion about "cleaner at the time of the FA" was explicitly about WCT. While I haven't done the upper pitches, I'm pretty sure, based on upper pitches elsewhere in the Nears, that there's an abundance of lichen on the face rather than moss. Top pitch of The Hounds is another good example of lichen obscuring a line in relatively short time.
Moss in the Daks? Sure, but that was just a passing reference by Seth. I have no idea how long it takes for moss to grow back on anything other than the roof of my house (3-5 yr).