Iranian plan B

Many units in 1st Infantry of 1943 had suffered more than 50% casualties during the Sicily campaign alone. From there it went to England and got filled up with - new recruits. Next mission was D-Day (where it suffered again around 30% casualties on day one).

Interesting, yet if this was the green formation sent in first to save the veterans for follow up operations why were the follow up units mainly troops who had spent all their time in Britain or new units that were dispatched straight from America to France?
Where are all these missing veteran units which were saved from facing day 1 on the beach?