So what I say is, the longevity of motorcycle helmets is 5 years only, if you store it on the shelf, in its original box, protected from everything.

Fact, touring rider motorcyclists put way more into the helmet.

Below a picture of the Marushin 999 RS, which I don't tell right now when - but surely bought in the beginning of the first season.

I cannot recall the exact HH:MM:SS, but I can honestly tell that in general I pay meticulous attention to my gear, especially on a tour.

Yet what experienced navigators immediately see, I noticed basically from one day to the other that the fluorescent colour at a relative constant point toward the Sun has faded out; my first assumptions have been the damaging nature of the UV-radiation.

Not directly because of the colour fading but its overall current performance yes, it's one of two gears to be renewed; pursuing the flip-up construction.

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Amateur but honest question: nowadays the flip-up helmets why cannot have a D-strap but only Microlock technology?