No living language has a fully authoritative grammar book, as the grammar of living languages is discovered, not prescribed. That's a part of what linguists do, after all, and they have plenty of debates over precisely how to do it. The overly-simplified grammars taught to language learners as "Correct" are only the tip of a huge, wonderously complex iceberg.
Here's an example of a more academic English grammar:
https://en.wikipedia.org/wiki/The_Cambridge_Grammar_of_the_E...
Note that The Cambridge Grammar of the English Language is almost 2000 pages long.
Yes, we agree, but those pretending they can when they are backed by governmental powers can go pretty far in term of influence.
https://en.wikisource.org/wiki/The_King%27s_English
Just a small sample:
"The 'split' infinitive has taken such hold upon the consciences of journalists that, instead of warning the novice against splitting his infinitives, we must warn him against the curious superstition that the splitting or not splitting makes the difference between a good and a bad writer."
On that subject: as a non-native speaker I always wondered if there actually is a grammar (not syle) guide which is considered authorative, as there is for other languages?