trevHCS:
In case you’re wondering why, its because class C was a new category on your licence so you needed a haz / theory test for that category to prove your basic knowledge base.C+E is just an addon to class C, thus its the same group and you’ve already done the haz / rheory tests for that category.
A theory test is needed for the first test done in a particular category group such as B, LGV & PCV