Well, after response from Probate office.....I contacted GRONI again a little while ago, said that whilst I fully appreciated now that it could be possible that relatives simply overlooked registering a death, I still thought it very unlikely.
As such, I thanked them for having already attempted to find a registration under, for whatever reason, a different spelling variation and/or entirely different name (and I too had tried online by adding a different 1st letter to the 2nd and 3rd letters of the surname and searching that way, but to no avail), but asked if that meant they could not offer any other hope of it being found by perhaps manually using the known date of death and checking again, all entries for that date, to see if any could have been 'my' chap. Anyhow.....have just opened my emails again and found the following reply:
I have eventually found the death registration which was incorrectly transcribed when the registers were computerised.
The death is */1923/***/****/**/**, the surname was transcribed as “Se***” due to the original handwriting, I have passed this to the technical team who in due course will amend the Index.
Result! 
So, it
was there, but with 1st
and 2nd letters of surname
incorrectly transcribed (think this adds credence to the need for them to allow for more variations of surname search than just 'equals', 'begins with (first three letters)' and 'variants', as even 'variants' did not pick up the name - perhaps allowing searches with no surname at all, as in this case, the forename and exact death date and area would have given me result/s that I could have then viewed and checked for possible matches).
ps
I know mis-transcriptions are always a possibility (I've done some transcribing in the past), but having only purchased 25 credits, ie enough for 5 certificates, that was the
second amongst my searches that was mistranscribed. Hope the ratio doesn't continue in a similar frame.
pps
The chap handling these mis-transcription issues has said he will forward an urgent note about the lack of response thus far to my 2 x 'Error Page' emails.
