Regarding the PRESENT PERFECT, the answer to how you use it is simple. The time is not known or unimportant. EX. "I HAVE SEEN that movie." When? I didn't say. Why? Why ask why? I didn't know or didn't want the listener to know, because the time was unimportant. The only thing that was important was the action of seeing the movie.
"I'm just tired of fixing all the damage that ill-informed "teachers" have done to students."
This air of superiority is not really too clever, Andrew. It will only alienate the students. Our policy here is to answer the question of the original poster, not to demean the answers of others. The original poster is usually smart enough to work out which answers are most valuable for him