Ximena, it would serve you best to go through the personal process of investing in the effort to identify these and their value. It is what we all do as collectors. You can Google stamp catalogues, find stamp identifier aps, go the your public library to find catalogues . In the process, you start understanding why we collect them. You are very good at photographing them. Go the next step https://www.kenmorestamp.com/us-stamp-identifier https://www.theswedishtiger.com/ID.html
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https://www.kenmorestamp.com/us-stamp-identifier
https://www.theswedishtiger.com/ID.html