Hello John
Hope this finds you well.
Just for the record (as the saying goes):
1. The 33 second clip from 'The Last Witness' is thankfully not lost but survives intact at the archive in Sydney. The confusion as to its existence seems to have arisen simply because it was never professionally transferred and a copy made for the BBC archives.
2. The team who put together the BFI disc would have dearly loved to have included this clip, but time and in particular the costs involved (which our have been astronomical and well outside their budget) was too prohibitive.
3. A fragment of one of the audio clips that survives from the The Little Black Bag was used to rework the ending of the surviving video material for the BFI disc (very cleverly too). The team would have been aware of the extent of the surviving audio clips, but once again the time and energy involved in cleaning up all of these and contextualising them to make them presentable / accessible (remembering that several are just simple fragments and also in very poor quality) would have been a mammoth task and arguably impossible to pull off satisfactorily.
4. The instrumental music and several sound effects from the episode Immortality Inc had thankfully survived because the composer - the late Tristram Cary - had retained a copy for his personal archive.
5. Regretfully I think we have to acknowledge that in all probability the late Alan Bromly had never had any tele-snaps of the third season of OOTU - by all accounts John Cura had stopped work in 1968 and would have been far too ill by the time the episodes were being broadcast in early 1969.
Hope this helps to clarify some the above points
Regards
Colin