Right - because this was a completely different era, and information moved infinitely more slowly back then (and up until Vietnam unravelled, people are way more reluctant to call out of the government on its shenanigans compared today).
Even so - actually it's a myth that most of these coups were even "secret" at time. By and large, the people actually living in these countries knew what as up. The Arbenz coup in 1954, for example (not on your list, but a canonical example of this "pattern") was exposed right away, and the US got a lot of flack for it internationally.
Anyway, it's not like I'm asking hard "proof" and the full operational details. Just, you know, some objective indication that there's something going on along the lines of what you're alluding to.
Which these days would be nearly impossible to hide for any length of time.