How can you tell what year Remington 550-1 was made?

Look on the barrel (just forward of the receiver) there should be a 2 digit date stamped on it. My 550-1P has a dollar sign five seven { $ 57 }1957 should be the year , Remington produced them from 1941 until 1970 all of those after the 1968 Gun Control Act should have serial, those before have no serial #.