Overprint Value Enhanced?

I have noticed some world stamps, as I stick them in my album, have overprints clearly showing years and some day & month. Does this really enhance the value of a stamp? by how much? or are they just curio? thank you

To be honest...it depends.

It really does depend. Sometimes parallel colours can affect value as well if they were released that way. Take a look at the King Ali issue from Saudi Arabia in 1925. It was overprinted with black, red and blue markings. Some stamps bearing the blue overprint can be the more costly of the trio (Scott #L184), and in some pieces the red overprint can be the more costly item (Scott #L169). Rarity is a big factor for determining the value of any collectible.

agree with knudson but withthe caveat rarity and demand decides the value

If they're Belgian stamps, usually this means a precancel permit, which show (typically) either a twelve or six month period. There are also examples with just the year in bold print.