It is true that stamps can be a clue to a time frame. I have collected stamps off and on over the years, but if you are trying to nail down a time frame, stamp may or may not be a clue, as any unused stamp is still worth it's stated value. However, if you have an old letter and can't read the postmark which is your only clue, I suggest you take it down to the library and look it up in a book on stamps. This means taking the stamp from the letter, holding up to the light to read the watermark on the stamp, then counting the perforations on the sides so you get a relatively fair idea as to when it was made. I have three stamps which are identical as far as the picture on it goes, but one is unperforated, and the other two are perforated differently. And, as far is color goes, yellows have been light, medium and golden on the same stamp with just a few years difference in age. The only thing a stamp on a letter can really tell you is that it wasn't mailed before the stamp was printed, but that it could have been mailed thirty years later. LeRena