@JasonMcD makes a great point. Sometimes we worry about the “exact” nature of things, but when it comes down to it, all the ABC Code is calculating is how often an item gets automatically counted. If you have an item that is borderline between an A & B, it might flip/flop every time you run the report. If you want, you can always manually override it at the warehouse level.
But also note, Epicor controls ABC at the WAREHOUSE level… an A item in warehouse 1 could be a C item in another warehouse. This could (and often is) appropriate. My “Finished Goods” warehouse has “A” items… the value of items in finished goods might be $1000s of dollars each. The “Raw Materials” warehouse has a bunch of items and all of them are less than $10 each. If we applied ABC Across the entire site, then none of my A items would be in Raw Materials.