We have previously discussed how boat builders regularly upgraded their safety standards as the industry grew a lot thru the 70's. Buyers started asking for more/better safety gear and racing rules started to demand it. (It seems quaint nowadays that at one time a sailboat was required to have one lifeline 18 inches high, and that was a move forward from no requirement at all. There was grumbling because the added stanchions and wiring added weight and also complicated sheeting in sails.
And some griped because it would make racing less manly....
I recall that some sailboat builders in the 70's would seize the lifeline to an upper shroud wire, since shroud chainplates were commonly rigged to the edge of the hull anyway. This eliminated one ($) SS stanchion.
Thru the 70s EY would use very detailed tooling for the deck and have mounting points for stanchion bases and pulpit bases, and IIRC there might not be a mounting boss in the deck surface for a midship stanchion on some models.
Noticed in your photo's: one shows a boat with early 80's Navtec turnbuckles, and lots of those were recalled due to failing w/o warning. I wonder if those were replaced? Second photo seems to show "closed" body turnbuckles, normally used on lifelines only. Not advised for standing rigging, but if I'm wrong someone can correct me.