As I recall the original negs were taken out of storage in the 70's to make a few prints to coincide the touring King Tut exhibition.
This probably accounts for the good condition of the negs.
I watched this last night having been a favourite for many years. No masterpiece but still very enjoyable. Anyone expecting much action will be disappointed as this is a film of ideas not action so it is very wordy. However most of the dialogue is very well written and worth listening to and...