Not only that, it is also well known that the smallest perceptible color difference (ΔE=1) is not actually consistent, even in the "perceptually uniform" color spaces.
So ΔE is actually 1 in some parts of the space, but up to 4 in others. However, that is "good enough" for the purpose for which these color spaces were created: quality standards for color ("can I buy more of the same color and it will look the same?"). If your measured and computed ΔE is below one, the difference will not be perceptible by most humans regardless.
And last I checked, new and improved "perceptually uniform" color spaces are proposed every couple of years.
So ΔE is actually 1 in some parts of the space, but up to 4 in others. However, that is "good enough" for the purpose for which these color spaces were created: quality standards for color ("can I buy more of the same color and it will look the same?"). If your measured and computed ΔE is below one, the difference will not be perceptible by most humans regardless.
And last I checked, new and improved "perceptually uniform" color spaces are proposed every couple of years.