Go by the sq ft first, if the county and seller are the same or very close I'd ask if the 3rd bdr was added by the previous owner. A conversion may not have had a permit.
Probably an error at the county, they concentrate on sq ft, not beds and may have been recorded wrong.
A lender usually does not check county records they go off the appraisal, that's their job. Title doesn't state it either.
I'd only be concerned with an illegal addition/rehab, and it may not be an issue in your area, so check with the county. It won't matter what it closed as last time. Depends on the county ho they treat such issues. Clear it up before you buy. :)