They were stamped specific to the Jetfire on the front pad. It is nice to have the correct number stamped in the block but other than that I do not think there was a difference. I would also assume that the Jetfire specific stamp is to identify it as a short block assembly and not the specific Jetfire block. If there is a difference I hope to learn myself.
The Jetfire stamps were also specific for 62 and then for 63.