There were/are different reasons for errors & especially on a DC.
I have a family, illiterate (possibly assumed through only speaking gaelic) as your Callaghans may have been ? which seemed to cause many errors through the language barrier as none spoke English & info. was taken by people speaking English.
I have 5 sons in a family born to my 3 x g g/parents who on their (sons) deaths their mother has 3 m/surnames
4 deaths were recorded by sons/daughters (g/children of mother), only 2 have it correct!
1 death recorded by an 'inmate' (actually an in-law)
1 of those deaths has him as 'widower' of...(mothers name with a different ms)...
Parents were father named correctly, mother...named as the wife (who was previously deceased), him being a 'widower'
I was able to ascertain different things to conclude those were the correct people/deaths through various other routes comparing ages/dates/names of wives/children (informants)/census' etc.
1 of the m/surnames given for my 3 x g g/mother on 2 occasions may be an indication of her own mothers' ms?
Depending on questions being asked, how they are/were asked can determine the reply which may not always be correct as we all perceive things differently with how things are worded & moreso if in a language one has little knowledge of.
Something else to consider is, in days gone by, many women who were widowed reverted back to their m/surname i.e. if g/mother was known (as a widow) by her ms it may have been assumed this was in fact her marital surname i.e. would be assumed the daughters' ms (in this case Catherine) was the same as her widowed mother was known as in latter yrs?
Who was the informant of Helen's death, did they sign or was it their 'mark x' ?
Annie