One of the interesting points mentioned on the pod was the repeated reference to "industry professionals". Indeed, the missing episodes of The Avengers appear to be in the collection of one said individual who was actually involved in the production of the show. My first thought when they said that there's one complete episode and a second (presumably incomplete), was that perhaps the incomplete story is the missing parts of the first episode? If I worked on that show and wanted to take a copy for myself for nostalgia then I'd probably look at either a first or last episode.
With regards to DW, if similar individuals took episodes, then I do wonder whether some of the assumed eventual returns might be episodes that aren't exactly expected as they may have not been retrieved from the ones skipped. Tenth Planet 4 for example, we know went missing somewhere between the archive and Blue Peter's production unit. Not hard to imagine a scenario where someone thought there was little point in returning it to be junked and instead just whisked it away for themselves.
Either way, based on what was said, one episode definitely in one collection, and "several" others in "several" collections - and they pointedly outlined that that's several episodes in one collection, several in another etc. Not just several spread across multiple collections. That would put the potential number at at least 5. And the hope is that this is just the start and that it may shake loose other episodes in other collections as and when people come forward for help with their own archives.
I can see how some people might have been a little disappointed as rumours had already started to escalate (I saw plenty of speculation that there would be 10+ episodes announced as found), but on the whole I thought the pod was very positive. Even 5 episodes would put a nice dent in the outstanding list, and could either complete a story, or perhaps even put an odd story into one that was completely devoid of episodes beforehand. Or perhaps it would just fill a few holes in the longer stories like DMP. Personally I would love to see SOMETHING from MARCO POLO. DMP 12 would be a huge find for me as well, and MYTH 4.
Certainly, after 12 years of Indiana Morris' vague and fruitless protestations of "lighting the blue touchpaper" and "wind blowing in the right direction", to have it confirmed that there are definitely more out there and possibly coming back sooner rather than later, it's a very good news day IMO.