What? What difference would it make if they read this or not?
As it stands, I'd assume you're not covered for anything not listed on the paperwork on the basis that phone calls can be lost. Given that, it's irrelevant whether they see this thread or not. Personally, I can't believe that Admiral would cover you for everything supercharger related and the massive power increase that goes with it for free. What did they say when you called them again yesterday to ask for everything in writing again?
Imagine how this conversation would go;
You - 'Hi I want to change my car from a Corsa SRI please'
Admiral - 'Ok sir. What are you changing it to?'
You - 'A Nissan Skyline'
Admiral 'Ok Sir no charge for that........off you pop'
Just aint happening is it!