No, there is no legal requirement to search for unrecorded amounts which may be due on a property, or any other unrecorded obligations (like to get renovations permitted) affecting the property. There is no reason a buyer couldn't search for these things (or ask an attorney, etc. to help him search), or that the buyer couldn't ask the seller to execute an agreement guarantying that there are so such things (so the seller could be held liable if they were), but doing the search is not legaly required.