Reading FCL.1025 throws up yet more poor drafting. For renewal the Examiner must have complied with (b)(2) which requires a Seminar within the last year of validity of the rating but gives no clue if you failed to achieve this.
For revalidation, it requires that you meet certain criteria within the period of validity of the Certifiate, but then within the subsequent text specifies they should have been completed within the lat year of validity.
In simple terms there really is no difference between Revalidation and Renewal.