Neither, it's more complicatedIn my timeline I didn't place "Carbon Creek"'s "past" parts in the 1950s but rather on April 12, 2152 where the framing story takes place. The reason for that is T'Pol speaking over the footage from the 1950s which to me signals that we are not seeing actual stuff from the past but a mere visualisation of the words T'Pol says to the others.
I actually didn't think "Carbon Creek" was that bad but it wasn't outstanding or memorable either. (quintessential ENT season 2) I do give it credit for introducing Mestral who made some cool apperances in Dayton Ward's (mostly) 20th century Trek nobels.
What about "The City on The Edge of Forever" which takes place in the 1930's?