You can print out more than 10, but only 10 are valid at any given time. There's a link at the bottom of the page with the codes to generate 10 more. I suspect

You can print out more than 10, but only 10 are valid at any given time. There's a link at the bottom of the page with the codes to generate 10 more. I suspect they do this so people don't print out 1000 only to be using 10 (or less) at any given time.