On BSAs and model 21s the lumps are dovetailed and soldered.
True, "BUT" that is a dovetailed Chopper Lump, not a dovetailed lump. On a dovetail lump the lump is all one piece & an entirely separate piece from the barrels. Inso far as I am aware chopper lump barrels have a joint in the lump whether dovetailed or not. Those which are not dovetailed are normally brazed, which I believe would likewise affect the welding.
I do know that some BSA guns had the dovetailed chopper lump, do not know if the all did or not. When just the term dovetail was used I was assuming this meant otherwise. The fact it is chopper lumped is what puts the joint in the lump, not the dovetailing.