How do you make sure they are?
First thing you do, you check the tin's label: it MUST say "Pomodoro San Marzano dell'Agro Sarnese Nocerino D.O.P.";
it MUST have a "N° XXXXXXX", which is the Number assigned to the tin by the Consorzio.
But even if all of these apply, the President of the Consorzio says they have seen cases where labels were printed NOT in Italy, completely fake. Of course! Who is here in the USA to watch??? Very complicated!!! So, what do you do?
As always, best thing is to shop from a merchant you trust!!! And look at the price. If it is too good to be true, it is not true!!!
Also, beware that the Consorzio says that San Marzano tomatoes can only come in tins; the tomatoes can only be peeled whole or fillets. Therefore, Edoardo says that if you see the words "puree", "sauce", "chopped", "diced", "organic" (also, not regulated by the Consorzio) on the labels, they cannot be San Marzano. Very complicated. Have questions? Send a picture of the label of your San Marzano and we'll ask the President of the Consorzio what he thinks.