The issue is who enters the code and when.
What I've seen work well is the tracking of complementary item orders, eg printer paper and/or toner sold with orders for printers.
First, determine the #/% of printer orders that include an order for paper/toner and average dollar amount of paper/toner orders.
Now you can provide incentive comp for higher frequency/higher aver $ orders for paper/toner.
The most reliable/most meaningful "code" is order mix/size either as stand alones or as complementary/secondary items to larger items ordered.
Hope this helps.
Bob Pastorini]
The Tele-Monitor Company
bpastorini@tele-monitor.com