the Enterprise was built when she originally was, in the form we saw her in TOS, but ...
She was destroyed somehow early in her existence
In the original outline, this would literally have happened: the ship destroyed in the opening scenes was not the Kelvin
, but the TOS Enterprise
, with Robert April in command. However, the writers were strictly forbidden from destroying the Enterprise
(even if they were going to replace it with a newer one), and Paramount ordered it changed to the Kelvin
and Captain Robau.