The Register is certainly providing interesting leads.
I searched for
Louisa A Mitchell with her known date of birth (25 Apr 1883).
This is what came up
Louisa A Mitchell 25 Apr 1883 Female Unpaid Domestic Duties Widowed 78 1
Madeline C Morris (Mitchell) 11 Jul 1913 Female Bank Clerk Single 78 2
When I viewed the Register itself there was little note next to Madeline's name.
London Gazette I.C.
What does that mean I wondered? Well who better to ask than Google!
So I type the following into Google.
london gazette madeline c mitchell morris
This was the first hit
NOTICE is hereby given that MADELINE CECILIA MORRIS of 3 Jubilee Court, East Grinstead in the county of Sussex, Spinster, a natural born British subject heretofore called and known by the name of Madeline Cecilia Mitchell has renounced and abandoned the name of Madeline Cecilia Mitchell and has assumed and intends henceforth upon all occasions whatsoever and at all times to sign and use the name of Madeline Cecilia Morris in lieu of and in substitution for her former name of Madeline Cecilia Mitchell; and notice is also hereby given that such change of name is formally declared and evidenced by a deed poll given under her hand and seal dated the 28th day of July 1942 duly executed and attested, and that such deed poll was enrolled in the Central Office of the Supreme Court of Judicature on the 14th day of October 1942.—Dated this I5th day of October 1942. MAWBY BARRIE and LETTS, 55-61, Moorgate, London, E.G.2, Solicitors for the said (177) Madeline Cecilia Morris.
As with any family history research you end up with more questions - why she did she change her name? And would I have found the change of name if it wasn't for the little note on the 1939 Register?