In looking at some original pieces, the old builders had the same problems we have today. The edges of undersides often appear to have been peened. 'Course its hard to say if those were part of the original forging process, but sometimes its pretty clear they are localized to possibly fill a gap. I started doing that a few years back and its good to learn the art of plannishing. Its the working of a metal edge to "grow" the metal out. If its real bad, then it takes a bigger hammer! But it really does work. And the face must be smooth. Try experimenting with a piece of metal to teach yourself how to do this. Doing this is not restricted to only the tang. It can be done on any metal part! It beats the heck out of glue-ins or epoxy fixes. But, if you have to do a glue repair, I use carpenters glue, BUT, its best to always pre-stain the area so the glue won't lock out the ability to stain.
Susie