Ellen,
Did you ever figure out how the in-house abstractor found the records? I find indexing errors (sad to say) pretty often when I research, and always let the C/R's  office know.  When they correct the (at least computer) records, the document is just deleted from one tax-id index and added to the correct tax-id index (if it is that type of error).  No explanation or notes, just correct the indexing system.  I recently was sent to fetch a doc specifically where MERS was a bene.  By index there was none.  But I pulled the open mortgages, and one of them had had the trustee entered as the bene, and MERS was not mentioned.  The problem was fixed, after I showed the computer record and document to a clerk, but no explanation, just "poof"  now bene reads MERS in the computer system.  And the next searcher will have no trouble finding it.  The request was from a company I worked with several years ago, and I think they might have been trying to salvage a no-find.  Well, I found it.
     Maybe your search brought upsome questions/corrections, and then the searcher (in house ) was able to find the correct records.  Just a thought. 
     To miss all those docs makes me think there was a big correction. Or part ogf the search was not completed.  Did you miss searching a name/spouse/co-owner? Or maybe part of the property itself?  In our county, if a property strattles a school district line it will get two seperate tax-id's.  One for each district.  Maybe something like this was the case?   Was the original searcher sick?  Not focusing? I'm really interested in knowing how the other docs were found and what the in-houser searched that wasn't searched in the first and second attemps.
   Like some of the other comments, I would offer free services and a humble apology.  Try to keep your reputation for customer service golden.  It pays off.
Sincerely,
Kim Haase