Short answer to continuity questions: There is none.
This came up yesterday. I was discussing Casino Royale with a rare fan: The kind who didn’t like Casino Royale. (And you know I absolutely adore fans with unusual opinions.) And one of her complaints was that the whole “prequel” idea didn’t work for her. She complained that Bond having been in love in the beginning of his career diminished his relationship with Tracy; that the whole premise of OHMSS is that it was Bond’s first love.
So, first of all I think if you feel that way you need to acquaint yourself with the novels. And second, I don’t believe a great and deep and tragic love is diminished by the notion that there was a love before it.
But more importantly, I have to correct this fan: Casino Royale is not a prequel.
A prequel is a story that jumps backwards in a continuity sequence to tell a story that happened in the past; often the first or “origin” story.
A reboot is a story that wipes clean the slate of previous continuity; all other stories are gone and never existed. Batman Begins is a reboot; it is not the story of Batman before he encountered Jack Nicholson as the Joker: It’s Batman fresh and new who never existed before.
Casino Royale is a reboot. There is no Tracy assumed or foreshadowed in Bond’s future when Bond meets Vesper (and I doubt they’ll ever write a Tracy). This is a brand new character. The other 20 official movies are self-contained, from Dr. No to Die Another Day, that continuity (such as it was) is over. I honestly don’t know why fans hook on continuity in Bond films, since it was always virtually non-existent. But there you are.
A major flaw of Casino Royale, I’d say, is that this was not made clearer to fans. Maybe this isn’t a flaw of the movie so much as of the marketing campaign. That, a year later, people still discuss the movie as a prequel means that someone at Sony didn’t do a good enough job.
So, for the record, there is no continuity between Casino Royale and any previous Bond film. And in a number of ways, that’s a great thing, but let me point one out that I don’t think has been mentioned before: The erasure of continuity means they can do it right this time, there can be continuity from CR to Bond 22, from 22 to 23, and so on. And that just might be really cool.