Stampfinder B01

Next: is the stamp overprinted or surcharged?

Yes
An overprint is a second printing on a stamp design, often in black or red ink, sometimes also covering old data. If it changes the denomination/value of the original stamp, it is a surcharge.

If the surcharge is only a suspected currency value or just a numeral, there may be nothing changing the country or usage. Still, click here:

Otherwise, click here:

No
Click here: