Modvat credit clarified: retrospective application permits credit on captively manufactured inputs from the rule's commencement. The explanation clarifies that Modvat credit is admissible on inputs manufactured in a factory and captively used for the manufacture of final products specified under the relevant notification; it makes explicit what the unamended rule already permitted and is to be applied from the rule's commencement, enabling settlement of pending cases and instructing field formations to act accordingly.