Sorry but I'm not quite sure I understand which section you mean specifically.
I've already read through the Date and Time Calculations in a mailmerge section and adapted the code given with 'MERGEFIELD Date' instead of DATE. I've also read through the introductory notes and date field basics. I refreshed the field as part of my testing and ran a mock mail merge using the month-end dates. It was during that testing that I encountered the aforementioned problems. We already use a DD MM YY system for example. From what I've read the only real change that is required is the above mail merge change, so my code is essentially the one in the DateCal V2_86 document with DATE replaced with MERGEFIELD Date.