I do this sort of thing a lot. You just need an equivalent line in the lower (blue) survey with -outline out to extend the blue scrap border to cover the white hole in your plan. I generally use an invisible wall line (so does not need '-outline out' option specifying) and make it slightly larger than the curved pit line so the overlap of the scraps is maintained even if a bit of distortion is applied due to loop closure corrections. As long as the scraps are in the same map level (i.e. not separated by a break) then the upper scrap will hide the overlapping area of the lower one. You cannot 'join' the scraps automatically now as neither will have an opening in the outline at the pit now. So if you need to join them to keep them aligned you have to specify the exact line points to join to pin the points at either end of the curved lines to each other in the pair of scraps.