Tax Code

[gainvidya]

I am trying to understand what tax code applies to me. Couple of ago year my p60 had tax code as 603L. I had some increment and last year p60 has 647L. Not sure am I on right tax code have I overpaid!

My friend got a letter from HMRC that he has overpaid and he will be getting £3K in refund.

Also I had paid £2K+ extra in 2003/2004 (worked for part of the year). I called HMRC if I can ask for refund and they said since I passed 6 years I cannot, wondering if I could still do something about it or just forgot it!