If I create an original file in Photoshop that's 8K, then produce a JPG of it, the JPG is both orders of magnitude smaller, and clearly a rendition of the same

If I create an original file in Photoshop that's 8K, then produce a JPG of it, the JPG is both orders of magnitude smaller, and clearly a rendition of the same work. There's no way to get back to the original 587MB 8K PSD from the 87KB 1024x768 JPG, but that's irrelevant to whether the latter is a version of the former. Just because the models are not perceptually the same as their training data does not mean that they are not effectively a lossy compression of that data.