Well I suppose Frederick might have two surnames on the marriage certificate, i.e. "Anderson otherwise Dennison", or the entry might have been amended later.
Anyway, it is indexed twice, let us know when you get the certificate!
Is this them in 1939? No more Anderson!
58 Kendale Road, Bridgwater, Somerset
Frederick A Dennison, born 16 Dec 1874
Eliza E A Dennison, born 21 Nov 1882
Maybe this death?
March 1966 Taunton 7c 261
Dennison, Elizabeth A. E.
Age 83
Which perhaps leads back to this birth!
DREW, ELIZA ELIZABETH ALICE
Mother's Maiden Surname: KNIGHT
GRO Reference: 1882 D Quarter in WESTBURY ON SEVERN Volume 06A Page 253