Every thing Ron said
I don't think your gun has been refinished, at most some cold bluing might have been applied but I can not be sure. This happens a lot. Some of the pits appear to have bluing in them but the pictures are a little glaring, so I could be wrong.
You might like to know there are at least two different 1900 Bulgarian crests. I think there is a 3rd one but am waiting for another example to show up.
Yours is the more detailed variation. The picture below shows a 1906, a 1900 that has been converted to a 4 inch barreled 9 mm and your gun from left to right.
Look closely at the 6 o'clock position of the crests and you will see an obvious change in the crest design.
Hope this helps
Vern