Upon opening a chest found within  a library in  a stronghold i saw a enchanted book with the enchantment loyalty 3 which cannot be gained in survival

Along with this in a survival world where i was afk fishing i got books of the following enchantments

unbreaking 2 and unbreaking 2 on the same book

and protection 3 and protection 3 on the same book

I've tested the stronghold loot chests 10 times and only twice it occured

and afked fish for approximately 2hrs and 3 books had enchantments which aren't possible in survival 

The easiest way to reproduce it is with fishing.However it may take anytime between 10minutes to 12hours