I'm sure they mean 71 world champions have worn AGV leathers over the years. Yeah, marketing hype, if you offer free leathers to enough racers some are bound to take you up on it.
I did spend a little while trying to work out at which point they would've been using the '71 Championships" for marketing, but I didn't make any progress.
Looking at the website it seems they started in '47 and seem to count car championships. Considering riders like Sheene, Roberts, Agostini, Mamola, Rainey, Cecotto, Luchinelli and Rossi have riden under AGV, plus drivers like Piquet, Lauda, Fittipaldi it could be just about any year.
Currently the website states:
"These collaborations have brought AGV many satisfactions and more than 130 titles..." but again, 71 titles could mean last year :-)
If it has a hump it's no earlier than about 2002.
If it has body armour including back protector built in then it's probably late ninties.
If it has originally-fitted knee sliders it won't be any earlier than about 1990.