the new rules do not state that already built fighters can be placed on newly built carriers (not specifically)
Page 21 of the AA50 manual, section “Where units can move”:
“A fighter may land in a sea zone that is adjacent to an industrial complex you own if you will be placing an aircraft carrier that you previously purchased in that zone.”
On Revised the rule was different, page 22, section “Restrictions on placement”:
"Newly built carriers can enter play withfighters aboard, whether those fighters were built this turn or
were already in the territory containing the industrial complex.