(Couldn't find the strike-through option to cross out my old post. I was in error when starting this thread. Mods, please remove it.)
An interesting take on it. The discount does apply to the Standard edition, but not the regional editions. You say you use Steam, and so we do benefit from a lot of sales. Perhaps Train Sim World 5: Frankfurt-Fulda will be discounted in October, and probably December too. Perhaps you could pick it up then. Until then, perhaps visit your Compatible Collection. There will probably be a route in there you have neglected for a while. Have a bash on your existing collection while you wait for the sale. Oh, and don't forget to collect the free starter pack while you're at it!