Excellent Nesta - thank you for the kind offer.
Those volume and page numbers only relate to the GRO system. (ie the mob now located in Southport). I believe that local register offices have their own system and the GRO numbers mean nothing to them.
We have also considered the possibility that Mary's death registration was never sent to the GRO, (therefore omitted for some reason) which means that it wouldn't appear on Freebmd.
Deb has given you all the facts that we know about Mary, however depending on where Mary died, and who the informant was, some/most/any/all of these facts may not have been known - possibly not even her exact age.

(so we probably need to be flexible with that too - as she had been so ill for so long she may have looked older than 50

)
Although she may have had cancer her official cause of death may have been something other than that (cholera? pneumonia?) so we also need to keep an open mind regarding that as well. When reading the diary there was so much speculation as to exactly what Mary's ailment was, that this is probably one of the main reasons we are interested in her death certificate.

The one
definite is the date and place of burial, so she must died shortly before 29 October 1847 and within a reasonable distance to St Anne, Soho where she was buried.
I am keeping my fingers crossed - good luck.
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Deb, you might be right about place of death as London rather than Middlesex. I will see how Nesta gets on, and give that a try if she has no success.
Re Granny Shepard ... I thought we had at least one possibility for her death registration, but where might it be hiding?