It's fairly easy to figure out how to fix things where I was the one who rearranged the code in the subsequent releases, but when someone else did it, the process becomes challenging. ClearCase was unable to figure out how to merge a large number of the changes, aided and abetted by the fact that our consolidator was rewritten to fix the locking problems by me in the old release and so that it could go into a DLL by someone else in a later release.
Some of those consolidator changes should have been compatible, but we used very different approaches to get to the same end, so they aren't. I've mostly been grabbing my older code and pulling it forward, then trying to figure out where to merge in any necessary changes on my end.
It's all merge-by-hand stuff and it is monstrously tedious.