Bear with me, I’m going to try to cut to the heart of the confusion here, which I think has less to do with how you interpret the rules and more about how you communicate with your players.
The definition of working patiently (BWG, 29-30): “Working patiently allows a player to allocate extra successes to the quality of a finished product. Extra successes can be used to embellish a description or add a flourish. They are largely a narrative device. However, many skills have their own rules for allocating extra successes…”
Seeing as Martial skills do in fact have their own rules for allocating successes, it seems Textually fair that working patiently successes could feasibly be spent as Add.
Intent Applies. An injury means nothing if it’s not part of the narrative - if you drive them off, and they are never seen again, what was the point of applying damage? As per working patiently, what is the narrative “embellishment/flourish” that injury applies? What are they actually asking for when they want to injure someone?
Do they actually want to capture or kill their attackers rather than drive them off? In that case, couldn’t that be phrased as their intent in the first place?
Do they want to hurt their attackers enough that the attempt cannot be made again? Why might the players choose this over killing them?
Or do they want to scare off others from attempting the same? To make an example of their assailants?
In my personal experience, sometimes players ask to deal damage in addition to their original intent just because it feels cool. Rather than simply say yes or no, I have to pause and take a moment to ask them what the function / purpose of that damage is, while keeping them excited of the potential of their answer.
This is not an accusation, but meant to be a gentle observation: Based on how you phrased your gameplay example, @Totally_Guy, it looks a little like you may have leapt to a conclusion as to what their actual intent was instead of asking them for clarification. I say this because I have caught myself doing this as well - and every time I do so, I make a ruling that feels anticlimactic or disappointing. I think the confusion of this post was brought on by the same mistake I make all the time - I forget to interview my players to decipher the difference between what they’re saying and what they actually want. By asking them these questions, not only might you gain clarity in terms of how the rules should be utilized in the moment, but you also give them a chance to express the nature of themselves and their characters in a way that makes communication easier in the future.
Technically, in accordance with the rules, Add is a viable way to use the Working Patiently mechanic, but doing so will not help your players learn how BW works and will likely create ongoing confusion in terms of how players and GM communicate task and intent to each other. In these moments, take the time to ask your players what they think they are getting versus what the rules will accomplish.