It's often been stated that the films have soft-rebooted over time; for instance pretty much the only constant in the first 19 films was Desmond's Q (and even he wasn't in every film, since he was recast from Dr.No and didn't show up in Live and Let Die for some reason). Still, the first 20 films are generally considered to be in the same rough continuity, although if you assume Bond is roughly 30 in Dr.No then he's about 70 in Die Another Day.
It kind of worked with Connery going over to Moore since they were roughly the same age although they didn't look much alike, but with Dalton that pretty much went out the window. Ditto with Dalton's Moneypenny, who went from the nearly 60-year old Lois Maxwell to 25 year old Caroline Bliss.
Even the Craig films arguably didn't totally reboot things, as they kept Judi Dench's M, although her role in Bond's backstory is definetly changed; in GOLDENEYE it was implied she was brand new and considered Bond the relic; where in Casino Royale that's kind of flipped (although Bond being obselete is brought back up again in Skyfall).
Also it's a bit unclear how Bond's personal Aston Martin in Skyfall somehow had the Goldfinger tech....although presumably he got it modified off-screen or during a "Craigverse" version of Goldfinger.