Since our friend harold WB9R just got a used TS-590, he was asking about 
how to tell it's age.  Told him I would post  info on the Kenwood s/n 
system:
Steve KW3A

* Taken from ts-590 e-mail list *
Starting in the summer of 2008, Kenwood adopted the serial number format
currently in effect for all nodels.

The first character of the s/n  is the decade of
manufacture (A = 2000 thru 2009, B = 2010 thru 2019)

The second character of the s/n is the last digit of the year of
manufacture.

The third character of the s/n is the month of manufacture (1 thru 9 =
Jan thru Sep, A = Oct, B = Nov, C = Dec).

So,

Serial numbers starting with B09 were manufactured in Sep 2010
Serial numbers starting with B0A were manufactured in Oct 2010
Serial numbers starting with B0B were manufactured in Nov 2010
Serial numbers starting with B0C were manufactured in Dec 2010
Serial numbers starting with B11 were manufactured in Jan 2011
Serial numbers starting with B12 are being manufactured in Feb 2011
Serial numbers starting with B13 will be manufactured in Mar 2011

and so, through B1C which will be December, 2011.

January, 2012, will be B21.
**