The HHonors website (under "Help" or FAQ) says to mail a copy of your hotel folio to the appropriate HHonors service center to get credit for missing stays.
I may need to do this, as I haven't received credit for my stay at the Singapore Hilton. Checked out November 28. Sent e-mail to HHonors a week later. Still no credit for the stay. (All other HHonors stays have been in the US and have posted very quickly -- within days.)
Kathy