Anjouan,
My apologies, you are absolutely correct.
If I may offer a consolation - operational regulations are retrospective (unlike certification); aircraft that have been certificated to Category A can meet the requirements that are specified. Those aircraft that have been certificated (by the UK CAA in BCARs or affilated regulations) as Category A (by default) meet the operational requirements.
Only if the operational regulations that you are using specify performance requirements (and some do not) do you have to manage this situation. On investigation, it may be clear that where the certification basis is not FAR/JAR compatible, there is a translation path on a once-and-for-all basis.
Such is the price of progress as a look into the complexity of AC 29-2C (guidance on certification) will reveal.
Jim