Sorry to raise this old issue but I too have a burial register entry for St John-at-Hackney for a Thomas James born 1795, died 1859, whose death cannot be traced in the GRO. I was lucky to have an exact date of death, i.e. 28 Feb 1859 taken from details of an inscription on the family vault found on the LDS film mentioned earlier in this chat and so requested a three year search by the GRO but without success.
The burial register entry for St J at H is for a Thomas James of the correct age and within a week of the death, i.e., 7 March 1859. Now that the GRO birth and death indexes are available, I have searched these and cannot trace a death confirming the GRO findings.
Of course, Thomas may not have died in the UK but was being remembered on the vault - his brother was buried in Blackburn and his sister in Eastbourne yet they are mentioned on the family vault so the burial register entry I found may not relate to the Thomas on the family vault.
Is it possible from your research numberfour that some notification of deaths in the Hackney Registration Office did not reach the General Registry Office?
Thank you for any thoughts you may have on this.