In the absence of any other possible, I too would take a punt on ordering that certificate
You have his d.o.b.
I searched FreeBMD for deaths ,
surname Lobeck
first name William
left the middle name blank
Death age/dob @1909-1911
and this William Ernest, with the 'exact' birth date you are looking for is the only one to come up from 1938 onwards
NB I also tried the same search with wild cards in the surname as LO*ECK , based on the fact the father completed the form and signed with the surname LOWEBECK for everyone, on the 1921 census Still only this one result
I've seen so many discrepancies on death certs with age, names etc I would hestitate to discount the one possible entry until I saw what is on the cert.
Boo