The discovery was made in November when the box at a bus garage in Birmingham was cleared, the Daily Mirror reported. The employees also found the young soldier's will.
Both were apparently left on a bus by a delivery boy taking them to the family in 1944.
Christine McDaid of National Express said she found the will and notice in an old box in the lost property office.
"The documents were still in their original envelopes unopened, so someone delivering it must have left it on a bus all those years ago," she said. "It brought a tear to my eye -- this poor lad had died for his country only a couple of months after writing his will before he set off for France."
Drivers for National Express had been trying to track down Heaton's family since November. A great-nephew of the soldier saw their news release while doing genealogical research. David Hall said he became interested in his great-uncle because he had been taking care of John Heaton, Gordon's brother.
Gordon was 21 and serving in the Royal Worcestershire Regiment when he was killed in the invasion of the European continent. In his will, he left his entire estate to his mother.
Because the notice from the War Office had gone astray, his family only knew for sure he was dead when the war ended in 1945, and he never came home.