WW 3 simply happened. Humans slowly advanced themselves afterwards.
Humans slowly improved themselves after WW 3, and then
they accidently ran into the Vulcans. Different scenario than from First Contact.
The Borg are still functioning, No one still knows how they work, and they were never bested by Starfleet (i.e Voyager).
The Q are still dangerous and mysterious. No knows how they work. (I.e Voyager)
No one still knows why the Klingons had smoother heads in the past.
If one series features first contact with a species, then that overrules what any other series may claim later on. (I.e Enterprise)
Humans didn't stop using money or eliminate want until the invention of a replicator-like device.