George VI’s Imperial State Crown was modified and reshaped for Elizabeth II. Metal was removed to make it lighter and the arches were lowered because that is seen as a more feminine shape. But the same gems were used and it is considered to be the same crown.
So, yes, what you are seeing in the old newsreel footage makes sense.
Thank you so much for the explanation—I could see that the same priceless gems were still in use. (LOLs about the comment above that the crown had collapsed.)