I own a Signature Edition which is one of the first ~100 Voyagers made. Never did see any inspection tag inside with a date. I don’t know if they used them in later Voyagers.
Probably the best carbon dating method is the datecodes on the ICs. Usually it is a four digit number YYWW where YY is the last two digits of the year and WW is the week number. IE 9912 is 12th week of 1999. The IC with the latest datecode puts you close to the year your Voyager was made.