User blog comment:KidVegeta/Canonicity/@comment-4363364-20140123122257/@comment-3097771-20140124020418

There are a few reasons. One, EOB was promoted as a spin-off, or a what-if scenario. From the perspective of the writer, it doesn't appear to have been an attempt to fit into the timeline. Additionally, it breaks canon in a few serious ways:
 * 1) Bardock was killed by Frieza. There is no way that in the Dragon Ball universe, being hit by a blast would send someone back in time. It's ridiculous and contradicts what has happened to every other person who's died to an energy blast.
 * 2) Bardock is completely out of character. He can't see into the future anymore, and his dialogue is inconsistent with his dialogue in his original special.
 * 3) Bardock cannot go Super Saiyan when or how he did. There are a few reasons for this:
 * 4) For one, if one considers the Broly movie canon (and I do), then Broly is the LSS. Either he or Goku has to go SS first. I usually place Goku as going SS first since the last Super Saiyan (1000 years ago), but Broly could also be the first. Bardock cannot.
 * 5) Bardock isn't strong enough or emotionally distraught enough to unlock the form. I realize that later in the series, Goten and kid Trunks unlock their forms ridiculously easily, but at this point in the timeline, no one is able to do it that way.
 * 6) Bardock cannot be the Original Legendary Super Saiyan. By original, I mean the one that was alive 1000 years before Goku reached Super Saiyan (obviously, since a LSS comes around every 1000 years, he wasn't the "first"). This simply breaks logic. By going back in time - an aspect of the plot already non-canon - he's being transported to a world that already exists. And the original Super Saiyan should have already been alive, as I doubt Chilled was alive over 1000 years prior to Frieza. So having Bardock go SS less than 1000 years after the previous LSS had is inconsistent with the universe.
 * 7) The people living on primordial Planet Vegeta are not the Tuffles. Tuffles look like humans with curly hair and slim bodies. This is repeated throughout the anime and even in the non-canon GT. Episode of Bardock changes this. And they can't be the ancestors of the Tuffles. They are too physically different to evolve into humans. Additionally, the Tuffles were a peaceful people; they wouldn't render those plant beings extinct or force them off of the planet. So this is very inconsistent with the universe.

Those are most of the inconsistencies I could remember. As you see, there are a lot of major things wrong, canon-wise, with this special. -KidVegeta (talk)