Thanks everyone, just want to update you of the latest development of my points & miles.

I've emailed Conrad Singapore and got dinged in the first two rounds of communication, from catering manager and manager on duty respectively, though I cited the event planner webpage.

Then I called Hilton Honors, the CSR told me that I need to talk to the GM or assistant GM directly since they are the only persons that have the authority to issue such points retrospectively (even HHonors CSR cannot do that!).

Then in the next email to Conrad, I politely asked the contact of GM/assistant GM, and received the response from its CFO within 24 hours that they will accord the points and miles "as gasture of goodwill and appreciation of your patronage".

Lesson learnt: ask to talk to the big boss !