GSW Tank age question

Does GSW use the 1st 2 digits or the 2nd 2 digits for the serial# for age indentification?

S# 9906489105 M#G84040TWA

It is either 1999 or 2006


I believe it is February 1999.

Usually, but not always, they use weeks (52) or months (12). So if you see anything greater than 52, that’s usually the year, so the other two digits will be the weeks or month. It’s common that if it is the month, then it is the first two digits. If it is the week, then it is the third and fourth digits.

So yours, with 9906, would be 1999, sixth week, or February 1999.