Are there special circumstances when getting sufficient glutathione in specific cells and tissues with GlyNAC will still fall short, so that targeted antioxidants will still be helpful, as when taking lutein, zeaxanthin, meso-zeaxanthin, or astaxanthin for helping with vision problems?

This is a good specific example of the likelihood at some point in one's life there will be special circumstances, due to aging if not some other chronic malady arising even at a young age, where nutraceutical support including potent antioxidants can be just what is needed to promote a healthy well-being status. So having such supplements as part of a routine regimen will provide useful coverage that can be relied on to head off problems.