Hello Neal,
Apologies for the late reply.
if I understand the situation correctly, the 300 additional items have been coded by one person only and you don't need to complete them through a comparison, right? If that's the case, you can complete them in bulk via the "Review Statistics" tab. In the "incomplete" section, expand the lines for the appropriate code-set and then click the the green "v" icon for each reviewer (doesn't work for the whole set, only for each reviewer). Repeat until there isn't any row for the current set and all the codings will have been completed.
To remain on the safe side, just in case there are some items that have been double coded but not completed, before doing the above I would create a comparison, complete all the agreements through the comparison, complete all disagreements via the "reconcile" button/window, and then proceed with bulk completion of all the remaining codings (as per instructions above).

I hope this helps!