Helmet strength.

My Shoei has a date of manufacture sticker. I CBA to look at the bell.

 

All of which misses the point that when everything else fails you will
have to rely on your helmet and its materials, methods of
construction, and retention systems, aspects of which had previously
been mentioned in this thread.

 

Nitro and OGK helmets certainly do, it's usually on a sticker inside
the lining (on the polystyrene).

 

I generally use whichever helmet is current until it's seriously too fucked
to use.

 

I tend to get a new lid every 3 or 4 years.