Andrew may have difficulty entering the KE/AF/Skyteam lounge at BKK. The Thai staff asks for an admission card the passenger is given during the check in process. The card is surrendered when entering the lounge. I suspect that unless departing that day on a Skyteam carrier access will be denied. As I understand the rule, C or F passengers are allowed access for their departing flights. Lounge access is also available for Sky Team Elite+ members who are departing on a ST flight. If Andrew is not departing on Skyteam he will probably not be allowed access, regardless of his status on NW.

Remember, you will be in Thailand. If access is not allowed, be polite and smile. Don't raise your voice or cause anyone to loose face.
Have a good flight.