IDKFA
I am Become Bilbo Baggins
Except a huge complaint is that people said Gandalf coming to ME in the second age DESTROYS canon, when Tolkien wrote that he was in ME as early as the First Age.
That is a valid complaint.
The definitive timeline for Gandalf's arrival is established in The Lord of the Rings. In the Appendices, it states that Gandalf came to Middle-earth in the Third Age to aid the free peoples against the Shadow. This was published material.
While Tolkien's later writings may have suggested alternative possibilities, these were never published works and most likely were never going to be (see previous post). Therefore, the Third Age arrival remains the established canon as intended by its creator.