Okay, you're still adding unnecessary complexity and, actually, making first aid much more powerful in the majority of cases.
The "treat once" rule exists simply to keep you from repeating treatment until fully healed.
A the end of a fight, you treat as many boxes as you can. If you're really worried that, after the next fight, somebody might get an extra box or two, mark the boxes as treated.
Tracking individual wounds makes no sense in an abstract system. The entire damage system is designed to be a simplified representation.
You treat a wounded individual, not an individual wound.
Treating the accumulated damage as individual wounds negates the vast majority of damage. You can simply do away with accumulated damage from minor wounds. Doing it your way would make Tanks, and really anyone with any significant amount of armor, much more powerful, as they tend to get worn down, rather than taking huge hits.
-Jn-
Ifriti Sophist