To be honest, labelling is possibly even more complicated than actually making yarns. And of course we cannot spin yarns about our yarns. Well, we can and do in describing the concepts, ideas and thinking behind designing a yarn, but not when describing the dimensions, weight and composition!
Also labels full of technnical information are not particularly photogenic, though we do try our best with Blacker Yars ballbands.
For semi definitive information, please refer to https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/513963/BIS-16-193-textile-labelling-regulations-guidance.pdf, although it specifically says one should read the legislation and that it is only guidance. Your local Trading Standards people are generally knowledgeable and helpful.