Brent
This old thread should help. I wrote an article for
GCA about the lost holes, but it doesn't seem to be on our website.
https://www.golfclubatlas.com/forum/index.php?topic=33878.0;Basically, Colt's original holes 6-10 on the New course were judged to be too steep, and the club hired Simpson to redo them in the very early 30s. However, Simpson’s holes were never popular, and the club then went back to Colt (along with John Morrison, who as well as being Colt's partner was a club member, and I think a committeeman) and they produced the current holes in the late 30s.
About ten years ago, then Sunningdale course manager Murray Long mowed the original Colt holes out. All the features are still there in the ground, as I found out when I went round the holes with Murray. The lost holes and the current routing meet at the tenth green, which is original, and which was adapted by Colt and Morrison to play from the current tee. The original tee is high up on the ridge, and when you stand up there, you realise that the green was very obviously designed to accept a shot from that direction. There's still some fescue on the old tee box too!