There are many reasons why the ∆E may be high in a situation like this. When you start stacking the various elements that can contribute to this, you’ve got: measurement device repeatability, printer stability (of each printer), mathematical rounding errors, the accuracy of the profiles, the instability of color around that hue hooking area. Maybe that last one being the greater.
This is a fascinating question. Theoretically of course, it is not possible to reproduce every color within another printer’s profile, since every color necessarily includes every combination of color numbers. In much the same way, you can’t define every single place on the edge of a ruler, because there are those little gaps between the 1/32 marks. This is sort of a problem of resolution. If you are talking about “human perceptible” color, then that might be a different story - you should be able to reproduce every color that is humanly perceptible - although I’m sure there are some who would disagree on that also.