This could be his birth registration date, two years after May’s, though only his marriage certificate would give a good idea of his birth year:

Surname First name(s) District Vol  Page
Births Mar 1894   (>99%)
READER Reginald Newmarket 3b 531
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There are only two Reginald Reader deaths in England from 1930 to 1990:

Name Reginald Reader
District Bath, Somerset
Date of Birth 1881
Page 0056
Volume 7C
Registered April - June 1951

Name Reginald Reader
District Cambridge, Cambridgeshire
Date of Birth 28th November 1893
Page 0948
Volume 9
Registered January - March 1978

My guess is that the second of these could be his, because it is not so far from Newmarket where they were married and where his wife later died.
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Their marriage registration date:

Surname First name(s) Spouse District Vol  Page
Marriages Mar 1924   (>99%)
Reader Reginald Webb Newmarket 3b 716   
Webb May R G Reader Newmarket 3b 716
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