You're right there Steve. I had a look at the protocol from 1917 and it does indicate that. Along with other oddities, for example having the consequence that neither Elizabeth and Margaret were styled as princesses until their father became king,

But I'd think it likely that when Charles declared back in 2019 his intent to slim down the Royal Family, without specifying how, that might have had a lot more to do with the fallout from his brother Andrew and family.