I’ve seen plenty of old movies in perfect HD and the make-ups stand strong.
But, I don’t think the drop in modern quality is due from the old masters dying with their secrets, I was just confirming Wooks suspicions on that subject.
It’s important to remember that not all old old-age make-ups were successful, nor are all modern attempts failures.
Back to the Future 2 proves that point. They had three different makeup artists do the old age makeup and they had differing degrees of success.