Right here. I bolded it, too, in my quote of what you wrote (speaking of lazy reading)
1966 is when the idea of social construct reached at least some of the population via sociologists Peter L. Berger and Thomas Luckmann in their 1966 book The Social Construction of Reality. That idea was used earlier in the 19th century, but very few people would have heard of it. You said the idea allows us to make those choices. I think people were able to make those choices long before that idea. What Kierkegaard and Sartre said are not connected to Social Constructivism. Both were opposed to social contructs with different emphases. The way you present ‘social construct’ is confused. It is not like a choice on a menu, but actually a mere habit in society. If you mean that once we realize this we are then free, you are still not in the same ballpark, but that would take a longer essay to go into.
In any case, well before the idea of a social construct was something people knew about people could make those choices, as the example of Kierkegaard certainly and likely Sartre too actually demonstrate.