By the very nature of making welded barrels, be they twist, laminated or Damascus, I am of the firm belief that any internal voids are closed up, &most likely welded. The same thing cannot be said of steel barrels of the era. POne is Far, Far more likely to encounter a "Seam" in an early steel barrel than a welded one.
I also fully believe that the fusion of the two metals does not leave a precise "Line" where this electrolytic Corrosion ( I presume the same thing as is often referred to as Galvanic Action) sets up. I read this often in print but it seems no one has actual proof of a barrel failure to which this can be proved to be its downfall.
