It has nothing to do with my argument, there could be awareness, to the extents that Unix architects had seen it in the news, but still, it was not considered. I don't believe support of leap second was built into Unix and honored properly until 1990s, when NTP became prevalent.
Also, the fact that Unix time starts before leap seconds were introduced made timekeeping in TAI an even stronger point. And I'm waiting for some insights on why it's not being done.
The change to UTC to include leap seconds was in 1972, which was after unix time came into existence.