One sliver lining to the pandemic is having time to catch up on software maintenance. So I finally got around to deleting/merging over 1000 item codes using this method, and the system has been working fine for a few days now. I'll do this now and then to keep things more orderly in IC.

I kept a backup folder of data before the changes so I can get historical data on the deleted items if I need it later.

Thanks to Steve for his advice on input formats.