Antti,
Parts can be resold: if I bought too many, and I don't need them, there are reputable resellers who buy overstock, and resell. After all, once I buy the parts, they are mine, they do not somehow still belong to Xilinx...no one is breaking any 'laws' here. Happens all the time (unfortunately).
What Xilinx does not do is offer support to companies who have parts purchased through resellers (as it detracts from the distributors, and it is impossible for us to warranty product when it has passed through a reseller).
Now, "not offering support" does not mean that you can not file a webcase. We are not going to check a part's pedigree for a webcase (unless it runs out that the part has been mis-marked, or mishandled -- see below). What it means is that if there is an issue with one of these resold parts, we do not honor the warranty, as the parts have passed out of the accepted 'chain of control'.
Something as simple as parts being unpacked, allowed to absorb moisture, and then sent off to a reseller, who then sends them to some poor user, who then assembles them without a proper re-bake, and has the packages "blow up" due to the water turning to steam in the solder reflow process is what we are concerned with, and what we have seen There are other issues with ESD, and other items that often can go wrong when parts are not handled properly.
I am sure if Francesco has enough friends, he might find a few parts to help him out? But to kit a full production run may be a tough thing to do on a moment's notice.
And, if you do get parts from a reseller, assume they need a full re-bake, regardless of how "well" they are packaged. You may want to test them before you use them, too.
(Even if you get them from your friends....)
There are (bad) people out there who remark good parts (up the speed grade) so they can make more money, and also folks who take parts that are not even our FPGAs, and remark them as Xilinx FPGAs. So in general, unless you have had a successful history with a reseller, Caveat Emptor!
Austin