We can now show examples of these labels which - as it is the Chinese Year of the Goat - show Goat 'stamps' in the illustration, and have the additional printing:
Of additional interest is the CARTOR caption on the goat, suggesting that these - and possibly our own Post and Go Faststamps - are printed not by Walsall in the UK as previously thought but by Cartor in France.
Maybe somebody can confirm which one of the International Security Printers factories actually prints for Royal Mail?
UPDATE 15 May.
Royal Mail have confirmed that although the labels advertise Cartor they were printed by the Walsall arm of ISP in gravure. Cartor do not have the capacity to print reels.
UPDATE 18 May
Thanks to George Wu of Taipei for sending more pictures including photos of the machine. George runs the Gulfmann ATM website, covering machine-vended postage stamps/labels from all over the world.
"France's Cartor Security Printing joined with British Royal Mail setting an exhibit booth at the 2015 Taipei Asian International Stampex from April 24 to 28, 2015.
"Cartor provided specially printed self-adhesive commemorative labels (no country name and denomination), and the Royal Mail’s Post & Go Series II machine was public demo during all the five days from April 24 to 28, 2015.
"It's a really new experience about the Post & Go system to all Taiwan philatelic collectors."
Many thanks George!