Marriage in Norwich, March 1936
Bennett, William F. - spouse Skipper
Skipper, Alice M. - spouse Bennett
Birth of a son registered in Norwich, Sep 1936
Free index to 1939 Register has, in Norwich
Alice M (Matilda) Evett (Bennett), born 1916
with Frederick W Bennett, born 1914
It means that Alice M Bennett later became Alice M Evett
Also looks like the son born 36 is listed.
The Evett birth alluded to in 1949 has the mother's maiden name as Skipper
I would examine the 39 Register entry, see if it says when they were informed of the change from Bennett to Evett?