I agree on the nylon. Other than UV (quite a lot of which comes though the average house window) there is no 'mechanism' for deterioration in a typical UK indoor environment if it's kept in the dark.There's a really easy way to find out
On the degradation of mono. I've seen nothing that says nylon degrades with humidity or heat cycling - where does that come from?
UV does degrade nylon with time. Just keeping it covered prevents that.
Fluorocarbon is unaffected by anything we can normally expose it to.
As for fluoro I can only make this comment. My 'early' Orvis Mirage went all sticky and came apart easily after about a year in a closed drawer in an unheated room.
(I've never purchased any fluoro of any brand since as after a couple of hours using the Orvis stuff I didn't like it so I put the spool in the drawer the next day.)