Per my rather long and rambling commentary on bug #34922, the remaining NULLs in the WMF revision table are really beginning to cause problems.
It seems that the script simply didn't work properly the first time, since the NULLs peter out in the morning of 8 April 2008, the same day the script was committed to SVN (r32937).
For reasons not yet explained, the NULLs only start appearing around 01:30UTC 4 October 2007.
Some revisions in that range has 'rev_parent_id's, but not very many.
Therefore I would suggest that the script be run again to cover thus period (give or take, revision IDs 162147000 to 204172300).