Unfortunately, due to a good old disclaimer at the bottom of all of the Games Workshop Legal emails, I'm not allowed to bring you the exact rules and restrictions as they were specified to me. What follows is a brief summary of what I understand that I am allowed to do and how I remain within these restrictions with the Rollcall army creator.
Thou Must Not...
An army creation app is not allowed to do the following:
The current incarnation of Rollcall (v6.1) and the ADF files available on this site follow these rules as strictly as possible. Rollcall has never stopped you from creating an illegal army (point 1). Rollcall 6.1 now doesn't even warn you if you are creating an illegal army (point 2). All warning messages have had to be removed, as an unfortunate consequence of the restrictions. The currently available ADF files (modified before the creation of v6.1) are also compliant in that although they will work with older versions of Rollcall, they will not raise error messages either (point 2 again). The current ADF files available from this site neither contain rules text (point 3) or devalue the Codex (point 4), from the understanding given to me in previous communications. Rules are only listed as titles, and a knowledge of or access to the appropriate armies list is still required.
Thou must...
Army creation apps must require access and reference to the relevant Codex or Armies book (although I assume encyclopedic knowledge of it is allowed too!). As stated at the end of the "Thou Must Not..." above, not everything is contained in the ADF files available here, and so access to the book is still necessary.
Final Words
I apologise to all those who came here wondering why their amazing army creation app didn't have all the features it could. Unfortunately the GW Legal Team don't allow army creators to do much more than just calculate points costs. Hopefully further communication and alterations will be able to bring the best possible Rollcall program, while still allowing me to distribute it freely on this website without the possibility of legal consequences!
Hive World Terra