Googling i saw people link to http://git.savannah.gnu.org/cgit/bash.git/tree/doc/bash.0 as an example of overstriking (albeit for bold not accents). The telnet rfc also makes reference to it. I also see lots of references in the context of APL.
I suppose in the 60s/70s it would be in the era of teletypewriters where maybe over striking would more naturally be a thing.
I also found references to less supporting this sort of thing, but seems to be about bold and underline, not accents.
nroff did do overstriking for underlining and bold. I don't remember if it did so for accents, but in any case it was for printer output and not plain text itself.
APL did use overstriking extensively, and there were video terminals that knew how to compose overstruck APL characters.
I suppose in the 60s/70s it would be in the era of teletypewriters where maybe over striking would more naturally be a thing.
I also found references to less supporting this sort of thing, but seems to be about bold and underline, not accents.