Recent experiences in the SIN SKL:
1. TG C boarding pass: Cheerfully admitted after initial confusion by SKL staff that "Royal Silk" was the Thai version of C class.
2. UA C boarding pass printed on TG stock for a flight departing nine hours later: Quickly granted access. I also thought I might try presenting an F boarding pass indicating "Royal First" for an upcoming LAX->SEA UAX flight.
3. Normal UA C boarding pass: Quickly granted access.