To be fair - Johnny Silverhand we meet is a heavily modified verison. Both memories, personality and (possibly) appearance are altered by someone, who may or may not be Yorinobu Arasaka.

Then there is base tabletop, creator of which (M. Pondsmith) is said to favour Nomads.

As an ignorant speculation, years may mean period of Archbishopship of Olinda and Recife, which is unorthodox choice for years in the first place.

Gentlemen.