Thanks, interesting, it claims the upper and lower are still there. Well if you want to direct someone to which end it will help but in the 70s the A-Z dropped the extra parts and they changed the official numbers (I drove a delivery van there soon after and had to adapt to it). But I don't know the exact year or why.
I finally got the answer from A-Z who explained only Londoners call it Lower and Upper, when it was built it was and always has been just Regent Street, as I saw in a 1922 map. Just shows.