I was one of those who doubted the value of GO too...

As a GO, at Y there has been <20% of the time that I was greeted on KA flights (and each was done in a robotic manner - no smile, <15s ), but on CX >75% I was greeted. On some CX flights, crew members even greeted me after taking off (as they were too busy beforehand). A very major service inconsistencies between the two. Sometimes, nitty-gritties matter to me At J, in my experience, everybody was greeted on both KA & CX. Having said so, food quality is more important than (robotic) greetings. It is sad to see the food and service on KA flights have been deteriorating in the past few years.

Back to your observations, perhaps a GO bag tag doesn't mean that he/she is a GO this year? Not updated about Singapore but in many destinations SL/GO/DM are in J line. That's why the line can be long...