16g is only assured up to that passenger weight - if you have a 300 lb. person sitting there, it'll fail at less than 16gs.
Yeah, and herein lies the inequity... If I STC approve a cargo net or other restraint for an item of mass which is not a person, I am required to placard a maximum mass to be restrained within. If I approve a seat, or a seatbelt, no such mass limitation - put in as much as you want! FWIW, my body mass is 185 pounds, and I ripped the seatbelt out of a 9G cert basis plane when I was crashed in it by my student two years ago. The seatbelt was found with a piece of broken off airframe aluminum still attached to it. My hip is not as strong as the seatbelt, they both broke....