I don't know the answer to your question Ian- though I imagine Johnnie Walker probably does.... but in looking to see if I could find an answer, I stumbled upon this account of the opening of the Holy Year, that has some superb photos of the Archbishop 'opening' the wall. You just need to scroll down past the 'headlines' at the top. http://www.newliturgicalmovement.org/2010/01/opening-of-holy-year-in-santiago-de.html
The one from Galicia (the round) and the one from Castilla & Leon. Individually numbered and made by the same people that make the ones you see on your walk. Discount is taken at check out, only by using this link.