Proving a fact when you just happen to know it

So I'm (re)writing an article and I know a fact, but I just happen to know it from collective reading over the years rather than a single reference. This fact would not be common knowledge to the general public and I would happen to know part of it from personal experience... (and selected reading which I can't seem to dig up easily or reference easily without launching into it too deeply to just prove that one point.)

What is the best way to deal with it in the article?

Fortunately it doesn't fly in the face of common knowledge. I just need to prove the "when".

The publication is a general publication so I can't get too technical or veer off.

The article is for laymen, not for those who would know the subject deeply.

And the audience is spec fans, though the subject isn't 100% about spec.

The tone of the article is a bit argumentative, but mostly informative to get people to think more deeply about the subject.

This magazine has published before things like "race" used in speculative fiction, etc. So it's more like that.

I'm being vague because I'm trying to keep professional about it...

Anyway, I sent a note to an expert to see if she knows, otherwise I'll use the thing the expert compiled as a rough reference, though it's not perfect.

This is one of the things that internally people know, but I can't seem to pinpoint to a singular event... I hope the expert will have better reference on the subject.