No-one knows how many episodes are missing - or what those episodes are. The Doctor Who Restoration Team do handle it with sensitivity. It's also worth mentioning that the BBC has a policy of not paying for the return of its missing material.

There are three things I took from the article.

Firstly, despite some fans saying the BBC should shell out for missing episodes, you would end up with a situation where private collectors could name their price. Just how big a price would name? It'd increased. The restoration team could be held to ransom for a long time to come.

Secondly, it has been reported that black and white episodes do sell fewer units (e.g. tens of thousands). Are there really that many of us who have a yearning for some of the missing serials? True, it'd be nice to have them, but I am not entirely sure I'd rush out and buy them. 

Thirdly, despite fan frustration, Southall made a profound point: Paul Venezis is a member of the Doctor Who Restoration Team. He has met with private collectors who remain anonymous. Southall argued that it must be worse for Venezis to actually know certain missing episodes are held by some than it is for us to simply speculate about what those episodes may be. Venezis knows what is missing. We don't. We can only speculate. Which is worse?

The whole "missing episodes" thing doesn't keep me awake at night. If someone out there really is yearning to own "Marco Polo" in its entirety, then I sympathise, but on many forums over time (I browse, but am not a member of any DW forums), it appears some are frustrated.

My philosophy is simple: I get on with life. I know that might sound harsh to the person yearning for a particular episode (and I'd love to see the Yeti story). If a missing episode turns out, that's great; but I don't anxiously check for "missing episode news" daily. If and when they resurface, that's great. In the meantime, there are plenty of hours of classic DW to enjoy.

Whoever these private collectors are, I think tact and diplomacy are paramount. Any hostility - or even the appearance of hostility - from fans or professionals is likely to drive them further into their "caves".

Approach them with a heavy hand, bailiff-style attitude - and they are even less likely to even consider negotiating. 

I wonder if there are efforts to locate missing episodes of other TV shows. DAD'S ARMY and THE AVENGERS, to name two, have missing episodes.

It's extremely unlikely that the Feast of Steven (which Rebecca refers to) had a film recording made but it can't be ruled out completely.

Paul Vanezis has indeed recently confirmed that "one or two" missing Doctor Who episodes are in the hands of private collectors.

Plenty of people are hunting for other missing shows. The organisation Kaleidoscope exists for this purpose and they hold events where missing material is screened.

Series two of Dad's Army wasn't recorded for overseas sale but two episodes were recovered in 2001 (they'd been made to show to a film company for the proposed film and were rescued from a rubbish skip). Three episodes are still missing but one has a sound recording which has been animated. One of the colour episodes only existed in black and white for a time but has been restored to colour using the chroma-dot technique also used on some Doctor Who episodes and the Are You Being Served? pilot.

For many years it was thought that the first series of The Avengers was lost apart from a single episode. Two more complete episodes have been found since 2001, along with the first 20 minutes of the first episode. The most recent find was in 2016 and came from a private collector.