One of our major customers requires that any sampling plans we use during receiving, inprocess, or final inspection be approved by them (the customer) to ensure that the plans are statistically valid and do not allow for the inclusion of defectives in the lot (C=0). It is a contractual requirement that is flowed down via their quality system requirements as stated on the purchase order.
I guess what you said leads me to my third possible assumption.
3) If you are using a sampling plan and your customer (by contract) requires that they verify the plan with them, then the customer must verify the plan before use (under that contract).
(Sorry for the gooderest English).
What you said makes perfect sense, I'm just trying to understand the meaning of the spec and transpose it into a procedure requirement.