#72: Nazi-occupation overprints on captive countries might have some historical value, as would the early stamps of the states that later made up Italy, Germany and Austria.
The same for the British colonial stamps such as the Gold Coast which became Ghana. When they gained their independence, a lot of countries including Ghana, overprinted their day of freedom on the old Gold Coast stamps. These might have an historical value too.
Confederate stamps, while often not worth too much, do have an historical value regarding the Civil War and American history (as does real Confederate money, newspapers, etc).
It all depends on what a person is interested in.
I have Greek stamps overlaid with the eagle & swastika; I was told they were worth less because they WEREN’T canceled.
I got sold off binders of coins years ago to put together a down payment on a house; they were recent issue, very common. I held onto pre-1945 stuff, as well as more recent ones if the countries no longer existed (Rhodesia, Upper Volta, etc.). Great way to learn geography/history as a kid.
I have dozens of uncanceled Nazi stamps, but I don’t think they are rare; one in particular probably is (Hitler & Mussolini facing each other from the sides, with the German phrase “One people, one struggle” on it.