SKU stands for stock-keeping unit
The key concept here is to make sure that each form of the same product has a unique identifier. This can be the universal SKU number (all SKUs are unique globally) or the older form of part number (internal use).
If you sold bulk, you would have one item number and one unit of measure, so you could tell the warehouse to send 14 pounds of item 12345.
If the items are in predetermined containers you would tell the warehouse to send 14 bags of item 12345 for one pound bags, or 28 bags of item 4567 for half pound bags of the same product.
You want the unique item number to contain all information needed to describe color, weight, size, type, etc.
Not sure what you worked out with Jason, but if the selection points to a unique item number, there shouldn't be any way that the selection would be grouped in with a different item.