To answer MrBreeze's questions:
I believe the switchover to the fake lock (as I like to refer to it) occurred in 1976 or '77. My '71 750 K1 had the button type until I brough it in for an inspection in '77. When I returned to pick up the bike, I discovered the swapped out part! The mechanic explained it was a mandatory recall. Seems someone had sued Honda after they had a major get-off and the tank cap popped open and caused fuel loss & burns. Don't know if there were multiple reports of such type failures, but I do have both types on some of my vintage Hondas. I'm keeping the push button on my K0-SL350 (as well as the after-market, float style, gas guage that's inset in an OEM style cap).
As to the headlamp on/off switch, right around '76 many states began requiring cycles run headlamps at all times. I believe you'll fiind most Jap bikes after that period do not have a headlamp shut off. I hate being so old that I remember this stuff - but like the fact that I can at least remember them!!! ;-)