Nip-It from 1973 was the last one featuring 2-inch-Flippers exclusively because there still was a little demand for the Bally Zipper-Flippers, which weren't available with 3-inch's.
Gottlieb was conservative and stuck on 2-inch until early 1971 with Now, the same way they were kinda stucked in EM from 77 to 79.