Source of title note vs. Description based on … note
One of these two notes is required.
If a good quality bibliographic record for the original format resource exists, you may use this record as the chief source. In this case, you will use a “Description based on <print/other format> version record” note.
If the resource is born digital, or if there is no good quality original format bibliographic record, then you would use the e-resource itself as the chief source. In this case, you will use a “Source of title” note.