The 18 for the basic set comes from the number assigned in the "Total Cards". If some one was to go in and change it to "100", basic set would only be complete at 100 cards (impossible for this set). The master set gets its number from the actual number of entries in the checklist - in this case, 19 entries. That explains why the numbers are the way they are.
Now, as far as the Brogna goes, I have no idea if it exists or not. More than likely, it doesn't if it isn't being reported by other sites. If you have done sufficiant research to come to the conclusion that it does not exist, go to the card's page, fill out an IR (inaccuaracy report) and give us details on where you looked (you have to convince Admin, once the resolvers have been convinced), and it can be removed. Thanks.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).