Mersey Rat is quite correct. "Yesterday" was already very well known in England because it was part of the "Help!" album released during the summer of 1965 on the Parlophone label. But it was totally unfamiliar here because it was NOT included in the Capitol version of the "Help!" album. It was released several months later as part of the Capitol edition of "Rubber Soul." The tentative intro by George Harrison on the Sullivan show tells you the Beatles themselves were always a little bit confused about the changes made by Capitol Records in handling their releases in America.
I never much cared for the revisions and adjustments made by Capitol on the Beatles albums. The Parlophone versions are much better, in terms of giving the listener an idea as to how prolific The Beatles were at their peak.