Any of your customers who work to the BRCGS Food standard will require the identity of the last manufacturer or packer, with clause 126.96.36.199 stating:
"The site shall have an up-to-date list or database of approved suppliers. This may be on paper (hard copy) or it may be controlled on an electronic system.
The list or relevant components of the database shall be readily available to the relevant staff (e.g. at goods receipt).
Where raw materials (including primary packaging) are purchased from companies that are not the manufacturer, packer or consolidator (e.g. purchased from an agent, broker or wholesaler), the site shall know the identity of the last manufacturer or packer, or for bulk commodity products the consolidation place of the raw material.
Information to enable the approval of the manufacturer, packer or consolidator, as in clauses 188.8.131.52 and 184.108.40.206, shall be obtained from the agent/broker or directly from the supplier, unless the agent/broker is themselves certificated to a BRC Standard (e.g. BRC Global Standard for Agents and Brokers) or a standard benchmarked by GFSI."
Since you re-pack the material, it should be sufficient for your customers to record your site as the packer. In reality, a refusal to disclose information about the supply route for input materials may result in your customer declining to approve supply because many food manufacturers who engage in BRCGS compliance also trade with retail customers (directly or indirectly), and there's an expectation of supply chain transparency.
Just anecdotally, I am not currently engaged in food manufacturing and I now provide software services... But in case it helps you to understand, when I was administrating supplier approval records for food manufacturers I would have strongly encouraged the purchaser to look for alternative sources for any raw materials if there was any resistance to my requests for technical information. I'd always be thinking 'why approve this supply route with the information deficit, when I can just put my foot down and have procurement find a more agreeable source?'
So.. I definitely think it's a valid argument to say your customers may not require that information for compliance alone - but refusal to provide it may still cost you those customers.