I was looking at the BBC News website earlier today and saw this article:http://www.bbc.co.uk/news/science-environment-11202019
(I recommend you read all of it and look at the pictures)

It's about fungus that can feed off the film on reels if they're not stored properly, you can see the damaging effect it if you watch a piece of film that is affected, now if that ever happened to the Doctor Who Archives my god there would be major uproar!

But the film will have been digitised.

G

But what about those that have yet to be made onto DVD?

Irrelevant.

G

What do you mean irrelevant?, if the original film is lost of a story that has yet to be released on DVD they won't be able to digitally restore it because they often start from scratch from using the original film.

As long as they actually HAVE been digitised. Has it been confirmed that they've all been converted?

@Who-Fan63, the content has to be recorded in digital form long before they can even consider compressing it down to DVD form.

Ahh I see...

I think nearly everything now exists in some sort of digital format.

Where lost material still turns up, it's usually 16mm film ("tele-recordings").

Note that, longevity is complex. Analogue sound recordings made 60 years ago are still fine, but early digital sound formats are now diffiicult to play. And, whereas a burnable DVD might last 10 years, commerically "pressed" ones last much longer.