Exactly. You could argue that God exists based on witness accounts.

I know god exists. elvis told me only last week, and the king never lies.

> I think it's incredibly important to remember that the plural of "anecdote" is not "data".

Honestly, where is the barrier between the two? I'm not suggesting it doesn't exist, just genuinely asking where it is, or at least where it's near?

Well, roughly and someone may have a better answer. Data is collected in a structured, systematic way, and the sample is carefully chosen. Anecdotes are not structured or collected in a systematic way, but worst of all the sample you've taken is the people who've chosen to speak up.

Anecdotes ignore selection effects. Data tries to control for them.

Why would radar recordings or radioactive soil samples not count as data (in the same sense that fossils are data)?

If we assume that the readings are actually showing a physical phenomena and are not technical errors or forgeries, they are still just that: an unexplained radar recording and an unexplained radioactive soil sample. There is no reason to jump to the conclusion that ETs are responsible.