The records for your shotgun indicate that it is an "R" or shell extractor shotgun. The "R" appears to me to be in the correct location. The gap between the last number and letter is usual. I am not aware that the Hunter Arms Company stamped an "R" on guns returned to the factory. I've seen guns that were returned to be fitted with single triggers and beavertail forends, and none were stamped with an "R".