Well, Fleming certainly ‘adjusted’ details like Bond’s birth year and other minor details about his backstory over time. But apart from a few small details, most of the loose backstory he established throughout the novels is pretty consistent with his final word on the subject - namely the obituary for Bond at the end of YOLT.
Basically, these are the two backstories for Bond that Fleming established.
As per the ‘original’ one, Bond is born around 1917 (he was 37 in Moonraker, which is set around 1954). At some unknown point of time, he joins the Royal Navy, eventually earning the rank of Commander. He joins the Secret Service in 1938. In 1939, shortly before the outbreak of WW2, he participates in a mission against Roumanians in Monte Carlo, which involves a card game. At some point during the war, he kills a Japanese cipher clerk in New York and a Norwegian double-agent in Stockholm. These kills eventually earn him his 00 number, by 1950 at latest.
And as per the ‘final’ version published in YOLT, Bond is born in 1924. In 1941, at the age of 17, he lies about his age and joins the Royal Navy to fight in WW2. By the end of the war, he’s earned the rank of Commander. After the war, he joins the Secret Service, and is eventually given a 00 number.
The major detail which changes between the two versions is Bond’s wartime service. Originally, Fleming envisioned him as a Secret Service agent during the war, but later retconned him as being in Naval Intelligence during the war and only joining the Service after the war.
But that can be easily reconciled. Bond could have carried out the two assassinations during the war, while he was part of Naval Intelligence. Maybe he was seconded to the Secret Service. And it was because of those two kills on his record that, once he joined the Service, he was eventually elevated to 00 status.
The one consistent element seems to be that Bond becomes 007 not long before Casino Royale. In Goldfinger, he says he’s been a 00 for six years…and Goldfinger is set in 1957 if I’m not mistaken. Plus there’s the ‘December Highsmark file’ of 1950, as per FRWL. So my guess is that this novel will be set around 1950…maybe a year earlier at most.