A brief update - not good news I’m afraid!
The source I had for the missing stereo episodes sent me his captures yesterday. Unfortunately, even though the VHS tape box had the stereo box ticked, the actual content appeared to be mono. Now I’m not sure if this is because the actual broadcast was mono, or if the recording was incorrectly labelled as stereo.
To clarify, I’m sure the information provided to me by the contact was genuine, just the tapes didn’t contain what he believed they did.

Anyway, the hunt continues.
PJ-1978 - I can see you haven’t been here since your original post, but if you do revisit at some point, please can you get in touch if you have any recordings of these 2 episodes that were made using a NICAM VCR. Thanks!

Again, I am also happy to look at the minor credits differences, but don’t have the ability to calatogue them since I don’t have access to original recordings. If anyone wishes to provide the summary of these I can see what is possible.