Thanks myluck for the welcome and the info.
My Mum was Cooper so I think it's going to be the same spelling and the Joseph and Mary birth dates are out by 4-5 years assuming the 1911 census is correct. I know I really need to wait for the certificates to arrive.
It's interesting the story of your grandfathers brother it may be that it's not possible to get some information because of the politics of the time as they may have been covered up.
Don't get too caught up on accuracy of spelling and/or ages
Keep an open mind on all records that are possible until you are sure they are incorrect
Literacy levels prior to 1920 approx meant that name variations were common and based on the scribe and how they spelt the name
Also at different times people aged according to their needs
Some aged dramatically to gain a pension; some remained young in the hope of marrying; some just were unaware of their actual age and calculated based on other factors.
Anecdotally - this week I heard the story of Jesse Owens the American runner; he was named James Cleveland Owens but when the family moved and he started in his new school the teacher misheard his strong southern accent when he said "JC" and registered him as Jesse and he became known as this ever after!