Hi! Compare the list of names in the email and the list of names in your active certificate. Read second and third sentences in the When You Get an Expiration Email section. Here they are:
We consider a certificate to be renewed if there is a newer certificate with the exact same set of names, regardless of which account created it. If you’ve issued a new certificate that adds or removes a name relative to your old certificate, you will get expiration email about your old certificate.
Hope that helps!