In my country they have to be called out on it, but to verify a discount, they have to prove that they were actively selling it at the undiscounted price for a period of about 4 weeks or so.
Unfortunately a lot of this is subverted by brands inflating the recommended retail price and then the stores just show a discount from RRP
They need to survive a month trying to sell something at inflated prices to then discount it. That generates losses for them - storage, space on the shelves, delayed new stuff etc. It's long enough to force them to actually discount shit.