There are 2 suggestions I can offer, and others may have different things to suggest:

1) Change the item description of unused items to 'No longer in use' or something similar, remove the 'Active' status on the item, and perhaps put an Alert on the item to pop up for entry staff, to suggest an alternate item code or other pertinent information.

2) I believe the program Item Number Changer for Adagio is able to merge items together (please correct me if I am wrong). You could merge all the items no longer in use into a single item called 'Outdated items'. This would hit IC transaction history as well, and I believe OE invoices and other locations too.