It's been clear for a while now that a long of big-name fans sincerely believe the rumors are true. I just don't know what that's really worth. In 1992, a lot of people sincerely believed that episode 4 of "The Tenth Planet" had been found. A few years back, someone managed to convince Ian Levine they had a copy of "The Wall of Lies."
Stead says he heard about these recoveries from the same source that told him about "Air Lock" and UM2 shortly before they were announced. (Which Paul Vanezis subsequently misled him about, causing a resentment that has colored Stead's response to these rumors and Vanezis' comments on them.) So it's coming from people who have had accurate advance information before. But being right once doesn't make you right all the time, as all the previously accurate spoiler sources who reported that David Tennant had signed up for series five could tell you.
I would love to believe something has been recovered. But the version that virtually everyone is spreading is still 90 episodes, and that's impossible to credit, especially in the absence of any explanation of where they all came from or why the secret plans to release them don't involve anyone who's worked on Doctor Who