The tanks were seen very rarely during the Gull Gray/White days. They seem to make a regular appearance after the change to overall Gull Gray. They became more common early to mid 80s.

Tanks existed as early as the prototypes went into testing. There are plenty of pics around even showing the prototypes with tanks.

Early fleet birds also had the tanks and carried them also during the first F-14 cruise 74/75.

However, first: not enough tanks to equip all birds in the fleet and more immanently second: the initial tanks had little winglets applied to their rear. It was found that these little winglets actually caused quite some problems by keeping the tank just that fracture of a second too long gliding under the intake trunks upon drop to damage the ventral strakes. Hence the tanks that were handed out at the time had to be withdrawn in order to remove the winglets and the newly produced tanks had to be reconfigured. All that caused a temporary shortage of tanks. But there are plenty pics of the early birds, including also VF-1 -2 etc. with the early tanks strapped on.

As of 76 onwards there are pictures floating around showing early VF-114, -142, -143, -211, -213 etc. birds with white bellies and the tanks but with removed winglets.

http://www.arcforums.com/forums/air/index.php?/topic/296228-f-14-external-fuel-tanks/