Hi Mike - hope all is well.
This isnt anecdotal as a friend of mine who purchased a "bargain" down in Algorfa had a issue.
He bought a resale on La Finca Golf last year. A nice property that was bought new in 2007 for €200K. None us need reminding about the price collapse and you can imagine he was pleased to pay €115K for it. The transaction went through and he paid the appropriate tax on the sale at the time which I think was about 10% on the €115k.
However he has been advised that he may now face a bill for the the difference between the €115K and the "Valor Castaral" - which is still €200K
His lawyer is engaged !
As you know one of the best around here Mike - ask J-Luis see what he says