Oh! Weird. In the follow up game (WARDEN) I actually remembered to put in, and it works like this:
Forceful: Add a +2 universal bonus to damage for your second strike in a round, and a +3 for your third and further strikes in a round.
The context being (when using this weapon) of course.
Thanks for the heads-up! I'll add this to the list of missing things I will ameliorate the next time I update the file!