The TT and Dt parts of the blanks will get hole sawed open, just like a lug has no blind holes. So any internal fillet is eliminated. But one does want complete penetration of the filler and a slight internal flow confirms this. By the same token I have no concerns about touching up the outside fillet after the initial brazing and filing. As we all know (famous last words?) it's the tube to tube contact and not the lugs that provide the strength of a lugged joint and not the strength of the lug/shell.

The lug blanks have about .009" to .016" of claimed clearance with the frame tubes before brazing the blanks up. During the brazing some distortions happen and that clearance reduces in spots. After hole sawing out the blind bottom the lug's ID can be ground to fit. Or at least this is what has happened for me before and what's going on with this set.

One could leave the lug with a bling bottom, so that the tubed don't touch directly. Then any internal fillet might hinder complete tube insertion. Not my idea of best arrangement. Andy