Re: Mine!
Not everything was made for the BBC on the basis of perpetual ownership.
With the older stuff made in a time before VHS let alone DVD the actor, writer contracts etc were based on one or two showings. While a sum would be paid upfront for this, if there were further showings, then repeat fees were due to those involved.
Hence if material from the archive is to be shown then there may be (admittedly small) cheques to be made out to the actors (or in the case of Daleks, Terry Nation's estate).