Just as a supplement to what Craig wrote:
It depends on how old the item is. There was an issue some time back around when the magic item registry was changed over to the newer issue of the expanded ritual database. The short version is that some items did not get correctly carried over into the version of the database we now have. Those items cannot be backtracked to because at one point there were two copies of the database, and one overwrote the other: a few months are missing entirely, and there are scattered blanks here and there. So relatively new items should be fine, and really old items should be fine, but some of the middle ones are gone. Blame Micro$oft Office. Or Ke$ha. If we can easily recover the item information, we can print a new tag, but honestly, we'd really prefer that people not lost the tags. For months now we've been pre-punching and laminating the tags that go out, and we can laminate tags on site if needed, so please just don't lose them. Even if we can find the tag it still ends up being something of a hassle.