Azure AD Premium P1 features without AADP1 license assigned

Dear community,

I have noticed that our Azure AD tenant overview shows that we are using Azure AD Premium P1. However, we have never purchased Azure AD Premium P1 add-on licenses. We use Office 365 E3 and E1 plans, which do not include AADP1. The premium features work, though. We can use conditional access, which is actually intended only for premium tenants, and we can also add a custom login screen with our company logo for Office sign-ins. We are a bit puzzled about how this could be. We have checked our tenant again, but we have never activated Azure AD Premium P1 for the entire tenant or assigned any licenses that include AADP1. Is there an explanation for this? Has anyone else been affected by this? Of course, we want to ensure that our tenant is correctly licensed and used, and we wonder if we are obliged to purchase AADP1 licenses, even though we have never made any configuration changes to our tenant that would introduce AADP1.

Thank you very much and best regards.