I have explained this many times in the past. When rubbers oxidizes, it is not like rust on steel where it attacks the surface first and works its way in. It is more like aluminium where it goes right through the cross section. Rust can be cut of steel and replaced with more steel. Aluminium has to be discarded, melted down to start again.
For those that tore down V2s, you would have noticed that greenie colour the grey mid-soles were turning actually went right though the rubber. And so this has nothing to really do with the parts being clear. The fact is, non UV stable products were used and this the end result.
What about no sun exposure? Doesn't matter. At some point, the parts were/will be exposed and even artificial lights like Fluro and LEDs emit UV.