:The alleged motive seems to be that it allows for backdating of property records.  Your family looks more prestigious if it bought something in made-up-year 810 rather than real year 914.  I have no idea how such a fraud could be perpetrated, though, considering that presumably everyone else would have to be in on it.  It's a stupid theory, but backdating your property records for increased family legitimacy seems to be the motive they're going for.