Leaf problem

No plant will ever have 100% perfect leaves, 100% of the time...........you are over thinking things! New growth is fine. A plant this size/age and growing in decent soil to begin with will not have any deficincies.........it should be impossible.

Over watering. Make sure to let soil get completely dry b4 watering also when you water make sure to water right at lights out

looks like burning to me.

Maybe K-tox? That's not normal progression for n-deficiency. In the more recent pictures, looks like that damage is not progressing, so i wouldn't react to it. Were those crispy leaves touching the substrate at one point? Any foliar spray used?

The end of 1 of your leaves looks missing 😄 as for the issue I would say nitrogen issue...