Did Mona have any siblings whose birth certs you could check?

Because William's name was so distinctive it seems likely that what I wrote in my last posting was correct, so an option for Charlotte Ann's different names is an illegitimate birth. This is just a guess, and probably only one of many possibilities:

1881 census (from FamilySearch.org):
Elizabeth COWLEY, Boarder (Head), Unm., Female, 27, b. Douglas, Isle of Man, Dressmaker
Charlotte A. M. COWLEY, Daur., Female, 1, b. Liverpool, Lancashire, England.
Source Information:
Dwelling No 50 Moon St
Census Place Liverpool, Lancashire, England
Family History Library Film 1341867
Public Records Office Reference RG11
Piece / Folio 3619 / 16, Page Number 25

Perhaps this "M" stands for her name given at Mona's birth? Her father at marriage could have been an invention to cover an illegitimate birth.
You could buy this Charlotte's birth cert to find out.

Len might help with refs in Lancs.

Sue