SG actually has the 6-month rule too https://en.wikipedia.org/wiki/Visa_p...y_requirements . But there is data point ICA will waive the requirement in similar circumstnaces https://www.flyertalk.com/forum/brit...l#post35823814

The bigger problem is not the border authority itself, but the check-in desk trying to CYA. They (CX HKG) might not accept correct documentation cases as correct https://www.flyertalk.com/forum/cath...f-mistake.html , so why bother with a case where they can easily point out what is wrong?

(Oh well, looking at the SG case, it may be open to your colleague to buy a cheap LCC from KUL to TH, where he is admissible. Then throw it away and try and plead for limited entry with Malaysian Immigration. CX will be within their rights to demand onward travel proof from TH, and your colleague will be gambling the whole trip that Malaysian Immigration exercised discretion and grants limited entry to your colleague. It’s a lot of work.)