Is it possible to only use cloud regions when registering point clouds pairwise? That way, you can clean up the point clouds before registering others. Handy for removing moving objects (cranes, trucks, cars, people), or even when monitoring to delete parts that have "evolved".
Or simply only register on a part of a building. Registration on a complete building (leaving all the PC's on) gives (numericaly) less overlap than on the only part that matters (turning some PC's off).
It would give a better view on how accurate the registration is.