Today, I found out that 987-6543210 is a perfectly valid Windows 95 product key.
Gigazine, "The product key of Windows 95 was implemented with an ultra-simple algorithm that can break through '111-1111111' and '000-0000000'", 2023-03-04: https://gigazine.net/gsc_news/en/20230304-windows-95-product-key/