It was 1940, before you comment!
But there's a serious point here. My father, born in 1926, thought the Battle of Britain was fought in 1941. I was adamant - knowing the overwhelming documentary evidence in my favour - that 1940 was the year. And I was surprised that he was so wrong, given his strong memories of the Blitz.
But then it struck me. His memories are of the bombing. And to a 13 year old, there's no difference between being bombed in the Battle of Britain and the Blitz that followed through the winter and spring of 1941. Oh, and unlike us, Dad didn't learn about the second world war in history. It wasn't history to anyone born in the 1920s. It was news.
The lesson, though, is clear. Don't take memories as gospel truth. Don't assume people who lived through the events in question can give you the facts. But don't trust your own assumptions about history. Dad's point was that Cardiff was bombed before London, and that his parents and aunt sent him to the Welsh capital for safety just as the Luftwaffe decided Cardiff was a perfect target. (The debate about the Battle of Britain is a sideshow.) Looking at the records, he's right. I didn't realise Cardiff was bombed before London.
But my point remains. Don't assume that eyewitnesses are flawless witnesses to history. In fact, don't assume anything...