I might be trying to tell Noah about the flood here, but for those interested, here's something that most don't know about this subject of parts and kit numbers, etc. There's a system of planning software marketed in the late 70s/early 80s called Manufacturers' Resource Planning or MRP. It wasn't the first of its type but it's probably one of the more successful, and it has several incarnations and evolutionary steps and competitors nowdays, and is the way a part evolves from a base material part number and quantity to a finished part number. I was working in the two-way radio business long before Motorola and GE adopted this stuff and have learned it along the way.
Don't know how they came up with the name or acronym, whatever it is, but it started with the original resource planning bills that become Bills of Materials. The chain of part numbers required to complete a part in the planning chain is the resource planning number. For instance, if it's a complete circuit board assembly ready to install, the part numbers will include the circuit board part number and the part numbers of all the components mounted on the finished board. This completed assembly is then given its own "complete assembly" part number that represents the parts and materials and manufacturing costs and the pricing structure. That's the number listed in the parts breakdown for the replacement board. The individual components on the board retain their individual part numbers for those parts that are available individually.
To install this completed board in a radio being built on the assembly line will require various and sundry pieces/parts like attaching hardware, wiring harness(es), standoffs, etc. This bunch of stuff plus the board becomes the "kit" number.
If a radio is built of several parts and kits manufactured in different places and by different vendors or company locations and then assembled in another location, the whole radio gets a "kit" number representing all the completed assemblies and parts that are required to complete a radio in the final assembly location.
All these multiple part numbers, assembly numbers, and kit numbers are the way they track how many of each of the individual parts they need, how many of the assemblies and how many of the kits will be required to supply the assembly lines and spare parts orders.
Sometimes the part may only be available as a kit because its easier and cheaper in many cases to stock only one part number, especially if the additional pieces are of minimal cost and they're buying it that way from a vendor or pre-assembling the kits. Sometimes towards the end of product support, you can tell when stock is getting low by the fact that individual completed circuit board is no longer available under its old part number, and now you get to buy the assembly line kits that weren't available under their resource planning part or kit numbers, but now the kit number previously not available is the "new" part number.
That was a simplified version of the real process, but hopefully it will get the idea across.
curmudgeon.....and I like it.