Did you date your search results for the same day?  Whenever we do any search, we date it back a few days because of the index not being "up-to-date".  In fact, we know of many instances where new systems delayed the index update by days, so this is always a good policy.  Also, do you provide any notices, disclainers or disclosures in your research reports which cover you?

Secondly, the owners signed a Deed of Trust (which is a type of contract).  They did so before a notary public.  In doing so, they finaized the contract in the form that it was created.  They showed competence to do so by being adults with proper identification who were not under duress, threat or coercion.  So, these signors alleged themselves under penalty of perjury to be the owners of land which they did not own.  Is anyone asking about their culpability in this process.  Also, who drew up the papers for them:  probably a title company or law firm, so how about their professional liability for providing legal advice as to the documentation? 

I'm sure that you were not paid a lawyers salary for drawing up papers, so the recording error appears to be on someone else.  The research question also begs the question of how a common man or member of the public could or would have reasonably know about a document recorded on the same day, if the index did not contain that data.  I doubt that a case can be made.

I'm not a lawyer, but I play one on stage, but only if asked nicely.  ;)