Hello Geoff,
Thank you for writing to us regarding your concern. Could you please confirm if you are trying to create the product group via API or UI and facing the issue of 1k max unique values per custom label? If you are performing this operation via UI and having difficulties, I would recommend reaching out to our product support team via help icon on the top right corner of your Google Ads account as they will be able to assist you better with all the UI related concerns. Also, it is not possible to create the products with different offer id within the product group via API. Please refer to this guide for more details.
Regards,
Nikisha Patel, Google Ads API Team