Connection to the big tree can be done in a variety of ways, many steps out from the profile in question. So say you had a family group of 10 profiles covering 4 generations, none of which are connected to the main tree. Only one of the profiles has to get connected before the others get connected into the tree behind it.
So you can always start with the original profile's change logs to see what changes could have been made, but in reality, it could be very tough to find for some groups!