So if I understand this correctly, “able-bodied” is a modified -ed adjective and “blue-eyed” a bare -ed adjective, which has brought me a new question: How are they different? They both look the same to me as adj + N + -ed, and the root words are “able bodies” and “blue eyes”.
No, the example Hirtle provides of bare (non-modified) -ed adjectives is "verandahed" (or the more usual verandaed). Another example would be bearded. Whenever the -ed component is preceded by an adjective (which is much more productive as a word-formation process), we call the compound modified.