The commonest cause for the informant is 'present at the death', usually a family member of course, and occasionally an unexpected one. When that is not the case - as maybe for a widow living alone - it may have been a nurse or 'carer', which can mean that the quoted age is several years out, as was the case with my gt-grandmother in Ireland.
I have another Victorian certificate giving the age as 77-3/4 (three-quarters). Unusually precise. Maybe she was very proud to have reached it, but it doesn't tally exactly with the birth data, about a year out.