Yes it has always been number 4, Ditchling Road originally began at the junction with Union Road and Baker Street, with the road running south to St Peters on the western side of The Level known as Brunswick Place. All house numbers on the eastern side are even, those on the western side are odd.
Numbers 2-8 Ditchling Road actually front onto Union Road opposite the north west corner of The Level, see attachment. Number 2 has a clinic in the basement whilst number 6 is Homelets letting agency. Numbers 4 and 8 are residences.