In this particular case for no reason other then that it's what happened 50 years before on October 9th 1965. While the Billboard 100 also tracks the biggest music market (which is, itself, not a tiny thing of importance) this was also, I believe, the first major list that Yesterday topped.The song wasn't released as a single in the UK until 1976 and never actually reached #1 then, it did reach number one in the Netherlands in October (I believe after the 9th but couldn't find the exact date quickly) and Norway in November though (according to Wikipedia :) ). 

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