STPC always worked like clock work for me. Book tickets, call EK and get the STPC vouchers issued and delivered to the airport, where upon check in I get them.
Once in BEY, had upgraded to J and so paid the departure taxes but forgot to pick up the receipt and the STPC voucher. The check in agent brought them to my seat on the plane.

I am surprised you never got told of the green voucher for STPC, or have things changed recently?