Did you get it? Trying to go through the process now and there isn't much on this forum about it recently...
I got mine last December. Went to Hanoi in person to apply, and went back to collect it, as I did not really trust them to mail it to me in a timely manner. I believe you could apply through post, but given I only had 60 days to finish the process (and needed PCCs from three countries), I did not want to invite more stress!
I lived in Vietnam for two years, and actually had a work permit. However, I did not have a copy of the work permit. I did however copy all the stamps from my old and new passport and make sure I provided dates that matched my residence as reported in my personal history. I applied on the 28th of December, and collected the certificate on the 18th of January. I believe we called to ask whether it was ready before I flew down to get it (as I recall I had a hand written receipt with a phone number on it). I subsequently had the translation/notarization done in Ho Chi Minh City (my wife is Vietnamese, and she had to apply for her police certificate there!). I imagine that could have been done at the Vietnamese Embassy in Bangkok, where I live.
If you need further information, I can probably remember/find more details as well as pick my wife's brain.
