The secret to resolving this issue is the Record of Service. This will summarise the entire history of your uncle's service.
The precise way of obtaining this record has changed over the years but the veterans agency website probably has some information.
If he is buried as you state, there should be a matching Commonwealth War Graves Record for him and this can be found online by calling up and searching the site - which is very user friendly.
Good Luck
Old Duffer