PortuGull
Gooooooooooooooooooooolll
Is that reporting correct?
In the UK, sell-ons are usually applicable to the DIFFERENCE between the original buying price, and the latest selling price, ie if Barcelona sold him to Getafe for €10 million with a 10% sell-on, and Getafe subsequently sold him for €18 million, Barcelona would be due to receive 10% of (18-10), so €800,000 (not 10% of the full €18 million).
I have no idea if sell-ons traditionally work differently in Spain.
Perhaps it would be easier to understand if you consider it this way: In South America (and perhaps this applies in Spain/Portugal but can't confirm) the selling club effectively retains a % effective "ownership" of the player; when said player is eventually re-sold that % then applies to the total resale price (and not the difference between original purchase price and resale price)