one of the many run-downs of the possible 'problems' involved in recovering any episodes that I'd heard was that a fan had followed the leads, got there first and got the prints, and was refusing to hand them over until the super-fans (Levine, etc etc) gave up the other episodes he was convinced they were hoarding (so the negotiations were about convincing him that they really, really, didn't have any).
This is a major problem even without a missing episode rumour. Some are so convinced there are more out there but not in the public domain yet they won't believe it even if they are told from the horse's mouth.
This really stems from the fact that it's already happened on three occasions;
1983 - Ian Levine returns Invasion of the Dinosaurs 1
after holding onto it for a year as 'bargaining material' should other eps show up.
1991 - Ian Levine returns unedited copies of The Time Meddler 1
; as the prints weren't his he didn't feel comfortable returning them beforehand.
2011 - The often repeated (by me) story of Galaxy 4 3
and The Underwater Menace 2
being kept secret for six months until the BFI screening.
You can see why some think the BBC / Levine / Vanezis / Roberts / the Beverley Sisters are keeping them secret...