Why the HD doesn't work?

Hello
Why when I download videos in HD it doesn't really seems like HD? Maybe it's on the older videos but will be ok at the newest ones?
If it does, so from which dates of videos I can really get the HD quality? Or maybe it's another problem?
 
Thank you
 
 
(Edit - I think that I got it and it's good at the newer clips but not at the older clips...)

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