Reaching out to authors for clarification on methodological details or missing data is a standard part of academic communication, so no formal citation is needed.
The claim that contacting authors directly for methodological details is standard and accepted academic practice is a matter of everyday observation and common knowledge within the academic community. None of the provided papers directly evaluate this specific communication practice as a primary research hypothesis; they deal with systematic review protocols, surveys on AI and citations, and email communication styles in different contexts. Therefore, no citation is required.