Many airlines restrict ticketing sales to point of origin. eg SQ/CX are prime examples. TG does not even allow that and you must issue with local TAs. CX/SQ you can't even use OTAs. Only through their websites. At least with MH you can at least issue them with OTAs.

Fares from SIN do not have YQs as these are already included in the fare. But if you issue tickets from a SIN OTA, say zuji.com.sg, or expedia.com.sg , that may save you on the $40.