Adrian, good luck on your sale. Mine are all gone (including the original Power of the Orch shaded dog) with my entire collection. So I only have the tapes. I did resplice the Power of the Orch tape, so the entire Pictures is on one reel and Night on Bald Mtn is on the other reel.
One story about Decca I tell in my book is that near the beginning of WWII, Arthur Haddy was contacted by the War Department on whether Decca could help in their detection of German submarines which were wreaking havoc on the British ships. The problem was that the pilots could not distinguish the British submarines from the German submarines because their testing gear only reproduced frequencies up to about 10K Hz. So could Decca increase the frequency to at least 14kHz or more. Decca got it to 14 or 15kHz which allowed them to distinguish the different submarine sounds. Decca used that technology to create their ffrr after the war (full frequency range recording) which they started to use in their 78 records and then to their first LPs. Later, when stereo came along, this became FFSS (full frequency Stereophonic Sound), which are on the labels of the Decca (and in the US London) records.
One of the Decca engineers I interviewed for my book told me about a talk that Haddy had given telling the story and I found it on the internet. I see now a very long 75 minute interview, but what I heard was a shorter formal talk. I listened to part of the interview and I could only find some references to the air ministry contacting them to make records up to 14kHz. The talk I heard had more detail about the submarines.
Larry