As most information for this site, the aggregate data from several sources. One is usually the county tax data. If there was a change in the deed, refinance, name change/marriage, etc the property will show as transferring (of some sort). It depends on how that county records their properties. Because of this, you see things similar to what most real estate websites call sales. Our county is notorious for having "sales" when all that actually happened was the buyer/owner cleaning up their deed information.