In the story, he took the flag from a balcony in September 1945. Just what he was doing there, and what the flag was still doing there months after the war ended, I don’t know. She didn’t get the flag until months after the war ended and there may have been some embellishment about where it came from. Clearly, the US officer didn’t get the flag from the Reichstag “before it was turned into ruins.”
Which the allies allowed to fly months after the war ended? Sorry, I'm not buying it.