While I understand the problem of the OP was already solved, there is another thing that might be a factor for someone else (coming to look for solutions to a similar problem):
Only five buttons on a mouse can usually be mapped directly: The left and right, press of the mouse wheel ('middle button') and then two of the auxiliary buttons (usually the easiest to access thumb buttons).
Buttons beyond that will not register as input, so in order to use them in game, you'll need to map them to a keyboard event in the mouse software. You can usually do this either globally, or on a game-by-game basis.
So if you wanted to map your third thumb button to "Full Map", you would assign it to the keyboard event "M" in your mouse software for the profile that's active with BFV.exe.