Can a less than 100% success rate be compensated for by including as part of the request in the Lightworker Healing Protocol, to have all prior spirits worked on who failed to reach the light be given another round of healing and rescue?

Indeed, that is a perfectly worded request to ensure they are not left behind and the client is underserved as a consequence. To continue this backward check, to address any and all spirits still floundering and who may continue harming their host, is a perfect answer and will solve the problem quite nicely.