Commonwealth War Graves Commission rectified 2 changes to their database after informing them about my findings.
Investigating the service records of Gunner Gordon Sinclair Fisher shows that Gordon transferred from 19 Fld Regt to 23 Fld Regt, Royal Canadian Artillery on August 29, 1944 (After he was miner wounded on August 21, 1944). The headstone doesn't need to be replaced.
Investigating the service records of Captain John Lloyd Johnston shows that he was Mentioned in Dispatches. The headstone doesn't need to be replaced.