The continuity error that bothers me the most is B-4 from Nemesis. We were led to believe that only Data, Lore, and Juliana Tainar were the only Soong-Type androids to exist, with Lal being a failed attempt. Then come the retcon of B-4. Data met Soong, as well as conversed with him in his programming, as well as met the Tainar android and Lore, and no one ever bothered to mention B-4. Very poor writing. I would have bought it easier if B-4 had been actually written as Lore.
I can suspend disbelief for the Hansens in Dark Frontier, and also Regeneration. The Hansens were just weirdos that others in the Federation considered crackpots, so any reporting they had done was seen with skepticism. We don't even know what findings of the Borg they even shared. Regeneration, I chalk up to Starfleet not knowing who or what the Borg was, and just recorded it as a one-off event, that was quickly forgotten since the Borg never returned.
But Generations never explicitly said they were refugees from a Borg attack. The El Aurians were there trying to get into the Nexus. For all we know, they were nomads long before Generations.
However, the fact the El Aurians never bothered to explain to anyone in the Federation why they were homeless, and scattered IS a continuity error. Why wouldn't the survivors be telling anyone and everyone about the Borg,a nd how dangerous they are? Especially if Guinan has been visiting Earth since the 19th century!
Very good points.