Marking something as reviewed is technically independent of providing an ID. You can give an ID and then unmark as reviewed (which I do sometimes when I still want to revisit the observation later). You can also mark as reviewed without giving an ID.
There is currently no way to filter out observations for which you have given an ID, only a way to filter them in (adding &ident_user_id=username to the search bar).
If there aren’t tons and tons, one workaround is to mark all observations as unreviewed, then filter for ones you have added an ID to, and mark those as reviewed. Then filtering for unreviewed observations is equivalent to filtering for those you haven’t added an ID to. For more information see https://forum.inaturalist.org/t/how-to-use-inaturalists-search-urls-wiki/63.