d-lass,
You failing to find his death registration on FreeBMD site Sunderland RO site does not mean much....1) The deaths on the Sunderland do not START until 1985
b) FreeBMD site only contains Sunderland Reg District deaths up to 1930.
You could peruse the GRO Death Index ( also sometimes referred to as St Catherine House Index) from 1930 onwards, until you find the registration.
Big libraries ( including Sunderland) have the indexes available for searching.
Some web sites have the indexes on line, but ususally for a fee.
And on the positive side, you won't have long lists of surnames to peruse, with Yewdell/Yewdle been an uncommon surname.
Michael Dixon