From what I was told, we have always been the engineering and design for our customers, but our customers have always headed the design process, taking full accountability. We were walking a fine line by excluding it from our original certification, but now we have customers that are requiring us to be certified with section 7.3.
If the answer is 'yes', then you are product design responsible. If the answer is 'no', then the customer owns the design. You may be a significant input to the process, but it's not your process.
Now, in terms of ISO certification, if you answered 'no', then all you may need to do is describe how you act on and interface to customers' design processes. But this shouldn't be under 7.3 of ISO 9001, since you aren't responsible, try 7.1 and 7.2.
If you decided you are design responsible, it's not just having a policy and procedures you need for certification, as I said. You'll have to demonstrate all the requirements of design control have been implemented. No evidence = non-compliance in most cases.
