Dear Ms. Scouten,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located Muster Rolls and Personnel Diaries, 1/1941 - 12/1980 in the Records of the U.S. Marine Corps (Record Group 127) that may be useful in identifying which units your father was assigned to. We also located Records of Ground Combat Units, Support Units and Other Commands, 1939 - 1950 in Record Group 127 that may include his unit records for this time period, although post-war unit records are are incomplete due to a lack of compliance in filing reports, and it is difficult to say if a flag detail would have been recorded in the records. For more information about these records, please contact National Archives at College Park - Textual Reference (RDT2) at Archives2reference@nara.gov.
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 RDT2. We apologize for this inconvenience and appreciate your understanding and patience.
In terms of the last American flag, this may have been simply a reference to the last flag of his own unit rather than the absolute last flag. There were Marine units in mainland China through 1948 or 1949. Also the American embassy was located on mainland China until 1949 and an American consulate was in Shanghai until 1950. With the restoration of diplomatic relations with the People’s Republic of China in the 1970s, American flags have resumed flying over American diplomatic posts.
The U.S. Marine Corps Muster Rolls, 1798-1958 are searchable on Ancestry with a paid Ancestry subscription. Some libraries offer free access to Ancestry to their patrons.
We hope this information is helpful. Best of luck with your family research!
[Information provide in part by Nate Patch, Subject Matter Expert]