Although NXWM E174 upwards will be '24' plates, the first vehicle actually carrying a '24' registration plate on the main site is First 36594, by pure chance I had to go to Leeds to fetch 6983 within 24 hours of it entering service.
Link here First 36594 (wmbusphotos.com) (https://wmbusphotos.com/FirstUK/30001-39999/36594.html)