As for eras, Connery through Dalton is all the same Bond as each has a reference link to Tracy. Brosnan is a different Bond, and Craig is yet another.
Could you imagine Dalton's version of Bond in MR or AVTAK - or even referencing those missions?
Okay, so "he was married once - but that was a long time ago." Fair enough, but in 1969 Dalton was in his mid-20s, and he wasn't playing Bond in LTK as if he was in his fifties. Just because his (and Brosnan's?) Bond was a widower doesn't mean his Switzerland mission happened twenty years earlier.
We accept CraigBond as a clean slate, with no Tracy trauma yet. Can't we accept that Dalton & Brosnan are a younger version of Bond with a different history from Connery/Moore? Did Connery or Moore ever seem so disgusted with the dirty world of shadow politics as Dalton was in TLD?
I'm not trying to change anyone's mind, I'm just explaining why I see Connery/Lazenby/Moore as one incarnation of Bond and Dalton/Brosnan as another.
And I notice that no one has mentioned the Q Branch scene in DAD as evidence that all the Bonds are one and the same - probably because no one wants to acknowledge DAD as canon at all. I would simply say that of all those devices are there more as a tribute to Desmond Llewellyn than to any one 00 agent.