The stamps are real; this is an unusual circumstance.
Only 2,018 L34 Camaro SS were built during the model year so it is a rare option. Of those only about 25% were automatic, 500 cars at both plants for the entire model year. To cover start-up production late in August planners had to have some stock on just about everything. So a small batch of JI engines were built at Tonawanda and sent to Norwood for stock. Many dealers limited stock on high performance cars over the winter months and the engines remained in stock. I have another L34/auto Camaro built later the same day in my db; has a T0102JI engine. Probably somewhere there is a May built Camaro SS L34/auto with the same engine date.
Low-option engines remained in stock until needed.