Sorry to throw a spanner in the works - but I reckon that Sidney isn't necessarily the Lambeth-born one on the 1881 census, but more likely the Aston-born one:
208 Mount Street Aston, parents Sidney and Harriett, Sidney aged 2 and Lionel aged 1.
There is a birth for Sidney H Cotterell in AMJ 1878, Aston area ref 6d 399.
This ties up exactly with the death of Sidney H Cotterell in March 1958 aged 79 years.