OAbot should propose new links even on citations which already have an URL, or green OA identifiers (like PMC and arXiv). because the new URL/identifier can be an improvement. See an example of good edit made after removing the if already_oa_param restriction.
Factors we can consider with small effort:
- for direct links to a PDF URL and certain identifiers, whether they're still functioning (CiteSeerX records and others can be taken down);
- for functioning links, whether they're identical to the resolved DOI;
- for identifiers, whether the existing identifier has higher priority than the proposed one (e.g., CiteSeerX identifier is less useful when there's already a PMC/arXiv identifier).