As I understood it, all of the Eurovision shows existed (within the archives of at least one countries' TV company o another) - except the start of the 1970 show (due to an error at the time). Hadn't heard of 1964 completely missing as well.
Well, 1956 doesnt exist on video unless the BBC kept their highlights programme thye allegedly showed the day after the contest.
The only clip from 1964 I've seen is of Gigliola Cinquetti coming down the stairs (Presumably after she won) to sing the reprise. I can't imagine that one clip survives and nothing else. I reckon RAI might have a copy in Italy but their archives are notoriously disorganised.