Therefore, it is impossible to call a shot when that happens and the bullet may not hit the 6 foot square target paper 200 yards away. There is no way to tell where the front sight appeared relative to the bullseye when a shot is fired.
It's possible to calculate it, or perhaps to make a table of where the bullet will hit based on various levels of sight misalignment. Most people would be totally unable to predict where a shot would hit with any degree of accuracy. They could say it will go farther left than intended, or higher than intended, but it is possible to get more precise if one puts some effort into it, I suppose.
None of that has anything to do with parallax using the definition you chose and linked to.
Both iron and scope sights have parallax problems when aim point on target, sight reference points and aiming eye are not on the same axis. Doesn't matter how far apart they are.
With metallic sights, there is no definable aim point when the eye is off axis from the sights. With the sights misaligned there is no aim point. Yes, the bullet will hit somewhere, and with a lot of work a person could figure out where it will hit, but there's no aim point.
When you're talking about aiming with metallic sights, it involves aligning the sights and the eye. With the sights and the eye aligned, the sights create an aim point on the target. When the eye is off axis, there is no aim point because for there to be an aim point, the sights and the eye have to be aligned.
I think what you're trying to say is that because the bullet will hit somewhere even with the sights misaligned that there must be an aim point. That's not true. If you pull the trigger without aiming at all, the bullet still hits somewhere--but there was no aim point.
Or maybe what you're saying is that because it is possible to calculate where the bullet will hit, or predict it with some other methods, even when the sights are misaligned, that there must be an aim point. But that's not true. If the metallic sights are not aligned with each other and with the eye, then there's no aim point.
I suppose if there are SMALL misalignments, then one could argue that there is still an aim point but that it won't correspond with the impact point. The problem is that it's not possible to say if that situation is due to the eye being off axis from the sights or the sights simply being misaligned. In other words, there's still no way to definitively call that parallax because it's impossible to know if the problem is the eye being out of the axis with the sights very slightly, or if the eye is in the right place but the sights are misaligned slightly.
Maybe it would be easier to start out with an answer to this question that we can all agree on.
If metallic sights are not aligned (let's say that the front sight isn't in the notch or aperture or maybe it is even completely obscured by the rear sight) what is the aim point?