Dear Guohui Jiang,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located the series Numerical Identification Files (NUMIDENT), 1936-2007 in the Records of the Social Security Administration (Record Group 47). As the Catalog description notes, access to these records is partly restricted under FOIA exemption (b)(6) Personal Information. You may contact the National Archives at College Park - Electronic Records (RDE) via email at email@example.com for more information about these records.
Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from RDE. We apologize for this inconvenience and appreciate your understanding and patience.
We hope this information is helpful. Best of luck with your research!
Thanks a lot! Very Helpful.