In 1840 the world had seen the first stamp and there were no stamp collectors or dealers at the time. So most of the issues had been used except a few that were unused by chance. Stamps issued in the period are called classic stamps. There are some differences in the countries, but the stamps issued between the 1840s and 1870s are classified as classic stamp. Those stamps are very high in value.
A stamp issued between the 1880s and 1900 is referred to as semi-classic stamp. The wide-spread collection had produced a lot of collectors and dealers. Postal stamps began to make a great deal of revenue. In those years there were countries that had issued stamps for the first time, but it was a time of philatelic development.