To me it looks like the circle marks around the outside are unevenly depressed - and also partially offset, so as not to form a perfect circle. Like you might see on some other piece of metal you hit with a crooked cutting/punching die multiple times.
But in the end it's not an interesting enough artifact for me nor an obvious part of the intentional design, so not something I'd bother to replicate on my ROTJ saber. At this point I'd really be satisfied with having all the correct basic proportions nailed (diameters and lengths/thicknesses/angles) on all the parts of a replica.
Agreed, it's definitely not a uniform circle. Some parts to me appear to be raised ever so slighly. Almost paper thin. This is something I would attempt.