Now there's a pre-war Vertibird in the trailer. Cool.
Many people have come to the conclusion that Vertibirds, being just in the prototype phase before the war and not having entered full military service, couldn't have been around then.
However, there were prototypes that were already used in the field.
http://fallout.wikia.com/wiki/Vertibird
So the rumor of retcon is now hopefully debunked.