There are indeed plenty of scams about, but perhaps best not to set them out here…!
I was indeed referring to Club World/First; no shorthaul flights get Arrivals access (even with a Gold Card) with the sole exception of the single early morning Moscow flight. I have edited my post to make that clearer.
As I set out, the “vouchers” are not “vouchers” but simply invitational guides to the location and facilities of the Arrivals Lounge; they do not permit access without an eligible ticket/Gold Card. There is a “voucher” system in place for the Concorde Dining Room within Arrivals, but that is handed out at the Arrivals desk itself.