Thanks, very useful response.
It led me to www.environdec.com which says: “Product Category Rules (PCR) are documents that provide rules, requirements, and guidelines for developing an EPD for a specific product category. They are a key part of ISO 14025 as they enable transparency and comparability between EPDs.” I’ll look further and see if I can find a summary.
Wikipedia says “Global harmonization of PCR and EPD standards remains a challenge.”