It'd be the daughter having the child in another country in the early 1970s.

I guess there is a good chance that there is no paper trail and a very small number of people that know any details and are still alive (because it happened 40 years ago, not because of anything nefarious).

If one were actually interested, maybe one could just look at all Senator's wives' daughters who traveled internationally in that timeframe?

Sure, I think that would be revealing. I think it would be a pretty large amount of work to make that list though, and it might not lead anywhere.

(like, did the daughter go there quietly for 4 months under an assumed name because the Senator was friends with a doctor...)

I suspect this information would actually be really hard if not impossible to track down. The actions of D-list celebrities, and I am not even sure a senator's daughter would qualify that high, in the 1970s is not reported like it is in today's 24/7 news cycle.

And, I can't imagine international flight passengers were tracked that closely either, much less stored for over 40 years.

This is starting to sound dangerously close to doxing (esp. if anything found is shared), even if it's out of pure curiosity.

There's a pretty big difference between speculating about what information to look for and actually tracking it down and publicizing it.

I don't think this really contradicts what 'digibo said. That comment seems to refer to the latter as doxxing.

That's how I read it too, I just don't think we are dangerously close to doing it.

But adoption records are probably hard to get.

The mother's name is redacted from the birth certificate shown in the story.

It's the link from that name to a Senator that is missing.