"50% or less", but at least something has to be 50% off and everything else could be less, otherwise every store might as well just put "Up to 99.999% off" lol.
Would it help any if they put those enhanced jewels on sale for a few days at 40 dias so that 20 dias would be 50% off? Heck, they can put them for for 80 dias, then 20 dias would be 75% off. Even better.
Lest you think I am being facetious, it is not that uncommon to mark something up so you can offer a discount. There is a store that I have never heard advertising at worse than "Buy One, Get One Free". That is their usual sale. Good sale is "Buy One, Get Two Free" and once in while they run "Buy One, Get Three Free". Something tells me they don't really expect anyone to buy not during "get free" period; assuming they even have one to begin with.