Good news for collectors of Prexies -- the presidential series of 1938 which was in use for many years before it was made yesterday's news by the Liberty Series: Scotts' Specialized Catalog of United States Stamps and Covers now list the value of the stamps on cover. (Readers of About.com Stamps know that on cover refers to a stamp that is on an envelope or other mail item.)
Collectors have been expecting this for over a decade and when news of the legitimization through Scott listing was whispered as a rumor, many collectors added a number of these postal history items to their collections. I'm sure that now they will be excitedly going to the new U.S. Specialized to see if their investment has borne any fruit.
Usage collectors -- that is, those whose interest is in not mint stamps, but stamps used in postal systems and collected as postal history -- find much to enjoy in a series like the Prexies, especially as exotic uses during war are plentiful. (Yes, the U.S. was involved in two wars during the years of the Prexies. Three if one counts the ongoing Cold War of the time.)
There is plenty of variety to collect in the Prexie area, including the entire set to the 50 cent value reissued with marginal markings to facilitate automation through electric eye reading. Another plus for the collector is that the series was issued in a number of configurations including sheets, and booklets and coils for lower values.