Are different countries old stamps worth a higher value?
The most valuable stamps are the ones that weren’t produced, or haven’t survived, in large quantities, so that there are more collectors that want one than there are stamps to meet the demand. Probably 99% of all stamps ever made around the world are not rare and don’t have much value. The only way to know is to be an expert. Those of us that aren’t experts use a Scott’s catalog, which you can find at just about any library, to look up what you have. Then, if you think you have one that’s valuable, you take it to a stamp dealer to verify it, because there are many common stamps with varieties that are rare – differences in perforation, color, printing type… – that the average person can’t spot but the expert can. So get yourself a Scott’s, and start looking them up.