Purchasing finished goods that contain preferred inputs, rather than the preferred inputs themselves, is perfectly acceptable and common practice for VCA investments. Certifying entities will need to work directly with Tier 1+2 suppliers to collect required documentation. For example:
Instead of providing a PO showing the quantity of finished goods purchased, you will need to provide a supplier’s PO showing the quantity of preferred inputs procured.
Alternatively, you may provide a letter or report from the supplier attesting to the use of preferred inputs in the finished goods purchased by your company.
See this link for more information about documenting VCA price premiums.