It would have been most unusual for a serviceman's record not to be annotated when he was listed as missing, not least because his next of kin would need to have been informed, and there would be implications for his pay and allowances etc. Any soldier missing for more than 28 days would be transferred to the Y List and this action would most certainly be recorded on his record.
Missing of course does not necessarily mean he became a prisoner of war, or if he was, that the British were officially informed by the Japanese that he was a POW. Japan did not ratify the 1929 Geneva Convention on the Treatment of Prisoners of War and so the International Committee of the Red Cross had very little opportunity to verify the whereabouts of missing servicemen.
That said, the National Archives claim that their records of WW2 Prisoners of War are 'virtually complete' so it would be surprising if WO1 Hirst did not turn up on any War Office casualty reports as either missing, or missing believed to be a POW, or finally as a prisoner of war.
More on TNA's POW records can be found here:
https://www.youtube.com/watch?v=5WvD_mI9CvU
