>To put another way, "guy was vaguely near New York on these dates" doesn't narrow down the search parameters by much.

That's why I said that this data alone is probably worthless, but can gain value when combined with other data.("As a piece of data alone, the results are probably not of significant use")

The combining of data is the important bit and the entire emphasis of both of my other comments.

Two pieces of otherwise anonymous data can, when combined, lead to re-identification.