Some time ago I asked how this oil of luck works and I got a partial answer. Well, the item falling out of the mob has a saved chance whether the lucky / lottery bonus will be or not. And here my friend could be right. Tested on around 20 Angel of Death Amulet. Some of them got a bonus for the first time, and the rest of them could sit for an hour and nothing.
In the case of gem making, it is more complicated. 1% / x to all attributes on the gem. Here, each attribute is considered separately. Separately Sstrenght, Dexterity ... Tested on dozens of gems.
If the item has the bonus added, you get it the first time you use the oil. Since the item is written in the code that the bonus will be granted and you get it the first time you use the oil, why are there two types, 20% and 40%?