I am 74 years old and in 1962 when I was living in Mexico City I went to see Lawrence of Arabia at the plush Cine Diana.
Many years later I found out they had to restore the film and even had to circumvent the problem of not having Alec Guinness around to re-do his spoken parts.
I am now a retired commercial and magazine photographer and writer in Vancouver, BC. I know for a fact that the film used for many years for making colour movies was basically a Kodak colour negative stock. This film is highly unstable. When you realize that the sound is part of that film you can understand the conundrum of keeping this film pristine. Movies are called prints because the original negative has to be sandwiched to make the positive used for projection.
In archiving movies the above has to be kept into consideration.