Severus Snape's copy on advanced potion-making is a testament to his intelligence, creativity and logical skills

Since he was a teenager, Snape has shown a remarkable attitude to making and brewing potions. His deep understanding of potion brewing, as shown by his expert concoction of Wolfsbane Potion in 1993, transformed the knowledge of potions from mere chemistry to an art. In 6th year, he modified an entire potion preparation book, these potions were very advanced and extremely complicated to prepare in the first place and by modifying the recipes, he produced much better results, results that he wouldn't have obtained by following the standard methods provided by the book. In my opinion, Snape must have spent his entire 6th year experimenting in his spare time, and it wasn't until his 7th and final year at Hogwarts that he was really able to put these recipes into practice. The Advanced Potion-Making book is part of the school program for NEWT students. Incidentally, here are the advanced potions contained in the book whose recipes Snape modified:

✔️ Draught of Living Death (page 10)

✔️ Elixir to Induce Euphoria

✔️ Hiccoughing Solution

✔️ Everlasting Elixirs

✔️ Poison Antidotes (Golpalott's Third Law)

It's surprising that Horace Slughorn never praised Snape's talent and always compared Harry to his mother Lily. He should have known from Harry's potion-making that the original work came from Snape. My opinion on this is that Snape was so secretive that Slughorn didn't even notice him during lessons, yet he became a member of the Slug Club, which shows that his talent was at least recognized although to what extent is unknown.

I'm sure Snape also modified the recipes in his potions books from previous years. I'd say that his talent for potions was far superior to Lily's, that he was clearly the best in his class at this subject. Quite frankly, Snape could have made a name for himself as a potioneer by revealing his modifications to the wizarding community at large, he could have written a revised version of every potions book published to the present time.