You have his service record held in ADM 139/787/38652 - the one that is blank.
The only other one I can find is held in ADM 188/4 which adds nothing to what you already know.
I don't see a Merchant Navy or a Royal Naval Reserve record for him either.
The blank ADM 139/787/38652 gives no indication of any reason why service is not recorded which is strange.
Regards
Hugh