Burnham
Woods walker
Looks like a offhand pattern...
I suspect the ultra short time frame is mostly a CYA move based on a worst case scenario.If you left a helmet out on the back of your truck in the full sun every day for two years then I could see some degradation. But in normal use and reasonable storage it should last much longer.
But if you get bonked on the head and the helmet fails, it lets the manufacturer off the hook.
You don't have to worry about UV degradation in New England this year. I'm getting claustrophobic just standing in my yard these days.
My Petzl is about 2 years old, so I'm due for a new helmet. I keep putting it off, though. Helmets are not cheap.