Sure, you add the first two numbers to the last one which makes 9, then you place the next to the last number to the right of the 9 which makes 90. Now you add the two middle numbers which makes 14. Add the 14 to the 90 (1990 +14) which makes 2004. There ya go!
I have information about the YTS-82Z tenor No. C70xxx, which was produced in mid-2009. Therefore, it is very likely that your sax was produced in the early 2000s. More accurate information can only be obtained on the official website of Yamaha.
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