Artificer level is not consistent.
Different recipes require different ratings. If you want to know what the recipe is that requires a certain rating, you can use the Wiki to look it up.
Good luck.
Low-rated items can be used in high-rated recipes. Once you’ve discovered the low ones, only the high will remain, given the appearance of inconsistency.
To show a bug, you’d have to demonstrate that something rated as Artificer 50 cannot be used in any r50 artificer recipe.
Here’s the recipe for Artificer Rating 50 Chattering Skull: https://wiki.guildwars2.com/wiki/Weak_Potion_of_Halloween_Slaying
And the recipe for Artificer Rating 200 Chattering Skull: https://wiki.guildwars2.com/wiki/Potion_of_Halloween_Slaying
All Artificer Chattering Skull recipes: https://wiki.guildwars2.com/wiki/Chattering_Skull#Artificer
You’ve already discovered the Rating 50 recipe, by your statement, so it won’t show up in the Discovery tab again.
Good luck.