One of my clients recently asked me if all customer documentation should be considered "documents of external origin", as defined in section 188.8.131.52 of ISO 9001:2015. I find this element of ISO 9001:2015 is often misunderstood. Here's a great article by Denise Robitaille that helps to clarify what is meant by "document of external origin".
Typically, any documentation provided by customers would fall into this category, or into 8.2 in the case of sales or contract information. For this particular client however, their customer was asking them to store their documentation (boxes and boxes of documentation!), and it was not being used to plan or operate the QMS. This is a critical distinction - if these boxes of documentation had to be considered documents of external origin, then they would need to be catalogued and revision controlled. Imagine the hours and hours of effort to do this, for little to no added value.
Instead, we decided to consider it as "customer property", which falls under section 8.5.3. In this case, my client now only needs to "exercise care" with the documentation instead of cataloguing and controlling it. "Exercising care" would include proper storage, adequate labelling and identification of the documentation, and protection from things like flood, pests, rodents, and fire.