@pelikano - to be honest I am not exactly sure what you are asking for?
Originally you asked to somehow separate the first match in each duplicate group. As others have explained I can't see how that is useful, because neither the formats nor the metadata associated with any particular book in a duplicate group can be assumed to be the one you should "keep", be it the first, last or any other. The only way to decide which one to keep is to manually investigate the associated formats and judiciously merging/deleting until you only have one book left. There are no shortcuts in this process without screwing up the quality of your library. I'm afraid you created your 4196 duplicates, so it is you that has to clean up your mess
Then in your last post you talk about "marking the doubles in a group or label". Again I don't know what you mean by that. The plugin already "marks" each group behind the scenes temporarily for the purposes of stepping through the result groups so you can resolve them, seeing only the duplicates in that group. You can step through the results and defer decisions on on group, and you can just run the plugin again to bring the results back up. So what is it that it doesn't do?