Portal stamp catalogs are important tools for obtaining postage stamp information. With them we can determine the following data:
- Year of Issue of the Postage Stamp.
- If it is a commemorative postage stamp, issued for collection purposes or for the circulation of letters.
- The estimated value of the postage stamp if it is "Mint", "Used", "In Circulated Envelope" or in "On First Day of Issuance with Postmark"
