Regarding the accident, he said he saw John only for an instant before the impact
As a student at high school (although it was many years ago…) I learnt that particularly the appearance of adverbs like: before, previously, a year ago, etc. in the sentence, necessitates using the past perfect, as they indicate the occurrence of one action in the past before the other! (And I remember doing endless exercises practicing that…) And now you are 'shattering the myth' for me!
High school grammar tends to include a lot of "always, never, must" etc., which are not really warranted in the real world of language. But it seems that such rules have allowed you to learn functional English, which I'm sure is the point of them.
Thank you for warning me.
It is a pleasure to learn from you!