Difficulty Bonus on Gear

So I started playing two days ago again after making a 6 months break and suddenly my gear has stats on it. This got me a bit confused and I don't know how it actually works, though If i have to take a guess, having Cloak & Dagger difficulty reduced from 50 to 30 would probably speed the studying process of it or maybe produce a bit more then it originally would? I'm also guessing both of these are wrong and It's a mechanic that Id like to get to know 
