Find your research notes.  Look over EVERYTHING.  INVESTIGATE FIRST!

You are not sure that YOU missed it. 

If it was a computer indexing error by the county, it may yet remain unfixed, or it may have been fixed in the mean time, but you have a right to the County's computer metadata that would show such index changes even long after-the-fact.    Use a public records act request to ask for such data.

If it's in old microfilm, microfiche, books or digitial reels, get the copies of both the indices and the reocrd itself..

Naturally, find a copy of your original report.  Did you use email or do you have phone records that you can use to reconstruct events?  Have a calendar out and keep a notepad and pen handy to timeline things;  you didn't research on a Sunday or a holiday;  what hours were your county offices open (have they changed hours in 7 years?), were there emergency closures or furlough days 7-years ago?  What contract did you have in place at the time?  Did it have good disclosures and notices about index errors?  Who actually did the work;  you or a contracotor or others?  What additional resources did you use to go beyond mere due dilligence in the Grantor-Grantee indices (or their equivalent) ... we all double-check multiple other resources like the Assessment / Tax  rolls, the GIS mapping systems, city records, building and planning permit records, and even things like voters rolls and private records too.

Do you have a written research methodology, written company policies or other things that might affect your research decisions?

Just some things to think about.