You may also be interested in R111, a similar report for individuals or R226, that reports individual user completions on each associated certification in the certification set.
Run R223 to view the progress toward a training path (formerly certification set) for individuals in selected user groups. You can filter the report to see specific completion statuses (e.g. Not Started). The HTML version of this report lets you drill down to individual details that can also be exported, essentially running R111 Individual Training Path Progress.
The image below is an example of R223 filtered to show one training path with ALL completion statuses selected.