ESRS E1 requires Scope 3 for material categories, meaning the sources that make a real difference to your emissions among the Greenhouse Gas Protocol's (GHG Protocol) 15 categories, and exclusions must be justified. The expected depth mainly concerns traceability: the data must withstand external verification. For major sources such as purchased goods (category 1), overly crude ratios based on spending expose the company to a qualification by its statutory auditor. To meet this requirement, it is better to start the assessment around 18 months before the first publication.
Read the source article: ESRS E1 GHG inventory requirements: CSRD after Omnibus