Replacing AP Crystal Check with XML - BI Publishing Checks

I have started researching the use of XML/BI Publishing to replace AP Crystal Checks.  I have gotten to where I can produce a .PDF file with the default PS layout.  Now I see there are basically 3 Report Definitions (APY2021X1A, APY2021X1B and APY2021X1C).  For the bank I was using, I had set the check form to be CHECK1.  I set up the Report Output to be XML Publisher, and when the output is created, it comes out as APY2021X1C.pdf.  My question is how does the system know which of the 3 Report Definitions to use (A, B and C)?  I