For The Love Of Port

Every bottle of Port I have consumed has one of those mostly white labels that have a number and some fancy graphical decoration. It goes over the cork on top and down both sides of the neck of the bottle and is visible below the cap or foil that covers and protects the cork. I assume this is some sort of stamp of authenticity -- "this Port wine really comes form Portugal and meets the requirements of the authorities that regulate Port wine!!!"

Can anyone provide more specific information about this stamp and what it means? Who controls distribution of these things? What does this stamp mean? What does the number on the stamp mean?

The who is the IVDP: http://www.ivdp.pt/index.asp?idioma=1&
That web site should have a lot of your answers, although some might be in Portuguese. The link I provided gives you the English version of the web site. I'll provide a very short explanation and let others elaborate. At various times in the history of port (lowercase intentional here), the quality of stuff sold on the market has deteriorated to the point where buyers became skeptical and buying decreased. And in just about all these cases some government or quasi-government authority has stepped in to regulate the production and sales to restore the quality. There was demarcation of the region, institution of the beneficio (not going to argue whether good or bad in the present day), and those labels. They indicate true Port from the region and validated to be of sufficient quality.

I've read a lot of the IVDP regulations, but not about the seals, so others are welcome to correct me.

When Dan Carbon of Symington was a guest here, I was trying to find out if there was any way to do two things: Get a bottling date for Warre's Nimrod (which unlike most tawny ports does not have a bottling year on the label); and, discover whether a bottle of port which was filled only about 3/4 of the bottle could be checked as to the bottling.

(What follows is my recollection of how he responded; any errors are mine alone.)
He said that there was an internal (not publicly available) way to determine from the stamp number approximately when a bottle was filled. He also hinted that they maintain video or pictorial records of the bottling line. These are incomplete and hard to search, so it isn't something they do on a whim. However, he seemed to indicate that the stamp number was either readable or could be correlated to the record in some way. My guess is that they are required to keep some sort of record, and this is how they do it. I also guess that they never (or almost never) have to refer to it, or they would make it more easily searchable. Maybe if someone made a credible assertion that they had found something dangerous in a bottle, and they had to defend themselves, they might dig into these records to refute it.

I believe that, for the consumer at least, one cannot tell the bottling date from the stamp. The bottlers buy these stamps from the IDVP and then apply them to the bottles at the time of filling. No coordination of the number on the stamp and the date of bottling. Each company probably has records I would guess.

Just for the record (since no one else has mentioned it), that stamp is called the Selo de Guarantia and is often referred to simply as the Selo.