Depends on the year, condition, etc. Pictures would say more on what you have.
As for rarely their not commonly seen, went too the NGD show today and there was one badly mismatched example there.
For the rarest one, I believe the 42 marked ones are the hardest too find only 32,000 produced in that year. The year of 1943 is the most common, 41 is hard too find, and 44 depends on what letter block.