I don't think it was ever in doubt, or really an urban legend. It was an openly reported fact at the time, in multiple newspapers, and confirmed by an Atari spokesperson. The Alamogordo Daily News ran a series of articles, and the main controversy at the time was local indignation that Atari might be dumping electronic waste in New Mexico without permits, which led to some changes in dumping laws. That a bunch of unsold E.T. cartridges were among the waste was reported matter-of-factly, and only seems to have gained mythical status sometime later, as a kind of symbol of the '83 crash. And then that mythical status morphed into people doubting that it happened at all! But now they dug it up and found exactly what the 1983 newspapers said.

It's being reported as having confirmed something that was previously mere rumor or legend, but it wasn't actually very mysterious or hidden at the time.