With the information here, I looked in the Scott Catalog, under Japan, found Scott # 339, then I had to open Scott Catalog under Korea to look up the information on the overprint.
Issued under US Military Rule, but what does that mean?
I am so confused, but in a good way

So, the original stamp, without overprint: Japan, Issued under US Military Rule, with overprint: Korea Scott # 59.
So how do all three countries, no wait, I am not even sure what I am asking or how..... So we have Japan, USA.. AND Korea?
So do they run the sheets through again, to add on the overprint?
And did the USA order Korea to do this and why? I'm so confused...
As you can tell, I know very little about history, but ah, stamp collecting has helped me tremendously!
What is a 'provisional issue'?
What is a 'specimen'?
Thank you!
SueStamps