USPS: How to determine the postage of older stamps?

Factual Questions
1

Here in the US, the price of a single, first-class postage stamp goes up every few years or so, it seems. Right now it’s 0.37, I think…maybe it’s gone up…I can’t keep track. Anyway, when I buy stamps, I usually stock up, which means I have the ends of books purchased maybe three to five years ago floating around in the drawer. The problem is that these stamps don’t have the postage amount printed on them, so even if I’m familiar with the current postage, I have no way of telling whether they’re enough. I usually end up putting two older stamps on a letter just to be safe. How does it work? If I buy first class stamps that just say “first class,” will they always be enough? Somehow, I doubt it.

Notes:

  1. We’re talking about normal, first-class business-envelope mail without special weight considerations. Just average bill paying stuff.

  2. The book I have right now, the stamps show a flag and say “USA First-Class,” with 2002 printed at the bottom.

2

Pop over to the USPS and look up the stamps you’ve got. The “letter” valued stamps were done as “we know the rate will be going up soon, but we don’t know how much” stopgaps.

http://shop.usps.com/cgi-bin/vsbv/postal_store_non_ssl/customer_care/qa.jsp?OID=8186