What is the difference between reporting "in accordance with" and "with reference to" the GRI Standards?
"In accordance with" is the full claim and requires you to satisfy all nine requirements in GRI 1. "With reference to" is the lighter claim: you use some GRI disclosures, say which, and make no assertion of completeness. Both are legitimate published positions — claiming the first without meeting all nine is not.
The nine requirements for an "in accordance" claim are:
Apply the reporting principles.
Report the disclosures in GRI 2: General Disclosures 2021.
Determine material topics.
Report the disclosures in GRI 3: Material Topics 2021.
Report disclosures from the GRI Topic Standards for each material topic.
Provide reasons for omission for disclosures and requirements you cannot comply with.
Publish a GRI content index.
Provide a statement of use.
Notify GRI.
The 2021 standards replaced the older "Core" and "Comprehensive" options with these two. If you see a report claiming Core or Comprehensive, it is following a version of GRI that is no longer current.
Requirement 6 is the one small businesses most often get wrong, and it is narrower than it sounds. A stated omission is compliant and a silent gap is not — but three things have to be true before an omission is even available to you:
Omission has to be permitted for that disclosure. It is not permitted for GRI 2-1 organizational details, 2-2 entities included, 2-3 reporting period and contact point, 2-4 restatements, or 2-5 external assurance. In GRI 3 it is permitted only for 3-3.
The reason has to be one of the four GRI permits, not a reason of your own.
The reason has to carry the explanation GRI requires for it, in the content index.