im not exactly sure of their birthdate. Why would that matter? Do you have information that you are holding back from us???? The mics were not new.
Please enlighten us......
Here are many answers from Shure on the SM57's over the years.
SM57 Shure answers 1 SM57 Shure answers 2 SM57 Shure answers 3 SM57 Shure Answers 4