Thanks again, Fg Off Bloggs, Your information regarding the lag time of the analogue CRC is interesting - I had not considered that aspect.
From what I gather, 809 experimented for a short period around that time with laydown at 150ft/420kts to improve accuracy.
It does appear that the Navy was a law unto itself - and I certainly don't mean that as a criticism either!
I tend to agree with your final comment: I am looking at how a technical failure might feature as a contributory cause, but cannot see it as a sole cause.