Well Tramadol got it's GSL as 'Tramal' all the way back in 1974 but it's so synthetically simple to make, when the patent potection ended, LOTS of nations suddenly saw it as a much cheaper than, say codeine or dihydrocodeine.
I remember it arriving in the UK, I watched the death toll go through the roof then then I saw doctors deciding that simple Co-Codamol and Co-dyrdramol might contain paracetamol - but that would limit abuse potential unless the user is prepared to play russian roulette with their livers,
Never quite worked out why hydrocodone never got introduced to the UK. My GUESS is that the BMC would designate ALL formulations as CDs and besides, dihydrocodeine does more or less the same job.