Hi
There was a William Johnston, aged 74 yrs. Harrowthwaite(sic), buried 4th January 1857 and Ann Johnston, 71 yrs. Harrowthwaite(sic), buried 11th February 1858 in Whitehaven Cemetery. Both were in common graves and both Church of England.
The ages appear about right and explains why they couldn't be found in 1861.
There is also a James Johnston, 58 yrs. 18 Howgill St., buried 16th April 1874 but he isn't at that address in 1871 though there is a family called Johnston ie. Thomas, 26 yrs and Annie, 28 yrs and Eliza, 1 yr.
There are some people who appear to be missing if they were in hospital (In 1861 all the patients in Whitehaven Infirmary were only recorded by their initials so don't show up by looking for a name).
I don't know how often this happened - obviously confidentiallity taken seriously even then! I have seen it with boarders as well.
Jo 3