Ok, I've had some concerns about the current Treat Wounds mechanic in how it has individual skilled healers have individual patients get bolstered from their individual treatment abilities. While from a gaming balance standpoint I understand the creation of a limiting factor, it seems like it would be a bit clumsy to explain within more pure story aspects, with needing to get a different, similarly or even less skilled healer to tend to someone.
What if instead of having the Treat Wounds skill cause a person to be individually bolstered on a critical failure, it instead imparted (or increased) a 'Treated' condition.
The Treated condition imparts a change in how skilled treatment applies. No wounds that haven't been sustained within the last 10 minutes can no longer be healed by use of the Treat Wounds activity unless the skill of the healer exceeds the treated condition as follows Expert overrides 'Treated 1', Master 'Treated 2', Legendary 'Treated 3'. This allows someone with higher skill to be able to miss more often before ultimately blocking treatment, or take over for someone with a lower skill, that whom they can no longer treat.
You might be able to add a new Improve Condition activity, that could supplement Treat Wounds. It would require administering some form of magical or alchemical healing, but allow a roll where, if your training exceeds the Treated condition as listed above. If your skill is at the point where you wouldn't be able to use treat injury, instead it would require a critical success and failure would cause individual bolstering of Improve Condition. In any case the only healing it produces, is that caused by the applied magic/alchemical healing.
Note: I also allowed the use of Treat Wounds to recover hit points recently gotten from the last encounter, even if they have gotten the Treated condition from a failed Treat Wounds attempt in the past. (although you could make it a conditional modifier on the skill check and/or healing result if you wanted it to have impact on that situation)
Treated condition would go away if healed by some means back to full HP, or otherwise by completing a nights rest where they would gain HP naturally.