I would also like to add..
...that continued production was with government approval , through the Defence Supplies Corporation. H&R would make runs of thier .22 parts as was economical , then assemble and ship after DSC would place an order , or to fill someone elses order who already had DSC approval. This was in place to produce what was needed during the war years to make the best use of materials and shop machines / labor / time. This is why production continued after the magic 6,000 number serial range. There are no records of the USMC placing another order , but it could have happened and has not been found.
Again , these are just best guesses based on limited known facts .
Chris