Way nice shovel covers RCs...and indeed you are correct..one is earlier than the other and the USMC specific belt hooks denote this......one is a depot made shovel cover and one is an issue shovel cover (later)
The strap buckles should bear this out......any evidence inside them of the PQD ink stamp or the USMC fiscal year stamp ?

The USS Miss one is possibly WW1 vintage...

Regards

Lloyd