I've looked this over in the Greek and the RSV as you asked and maybe I'm just not getting what you're driving at here. What has this got to do with Mary's status as Co-Redemptrix?
The objection to Mary sharing in redemptive work is, IMHO, in the same “family” as the objection to Paul’s making up what is lacking in the sufferings of Christ
There is nothing lacking, and how could a sinner make it up if there were? Yet here we have the text.
So, I think the answer to one is likely to be in the same family as the answer to the other.
And, as I have said so many times on this thread that I’m afraid of being ridiculous, the answer is that it is not just Mary or just Paul. It is them in Christ, and Christ in them.
This is at least 5,000 word paper stuff, which is why I end up being so elliptical.