It would be helpful to know the make of your gun.
You put "DAMASCUS" in all caps in the title of this thread, but have not told us if you can actually see a Damascus pattern. I have a Grade 2 L.C. Smith that has reblued Damascus barrels. The seller told me it was fluid steel, and it sure looked like fluid steel. But after I took it home and fired it, I then noticed the Damascus pattern under close examination in bright sunlight.
Sometimes the pattern of the welds and layers of iron and steel will show in places where the reblue gets rubbed thin, such as from contact with the forend wood. Alternatively, you might rub a hidden area with fine steel wool and a mild acid such as vinegar to reveal the pattern of the Damascus. If the gun has been reblued, such testing isn't going to really hurt the value. But just do a small area, and don't slosh vinegar all over, because it will completely remove the blue If left on long enough. If this is a turn of the century cheaper Belgian import, then I wouldn't put much stock in the Siemens-Martin Chain Steel stamp. Some lower end Belgian makers were not unlike the Chinese today when it comes to producing cheap knock-offs with misleading stamps or names in order to convey higher quality.
Of course, some close up high resolution pics of the gun, barrels, and barrel flats would be a big help. Assumptions and wild guessing won't accomplish anything.
