Accuracy doesn't imply 100%. A lot of hard scifi, from the classics on up to your modern stuff, hinges on the speculative and a lot of it you can't actially say "it can happen".
I mean, Jurassic Park (the novel) is hard scifi. Even when it was written, the idea that dinosaur DNA could survive to be used as it was was entirely fictional; it was an enabling device.
What made JP hard scifi is that what that device enabled was accurate; the dinosaurs were at the time the most accurate depiction put to screen or print.
Where you start to cross out of hard scifi is when not only accuracy has been handwaved, but logic and internal consistency, both of which are more important. Accuracy is flexible, but things have to follow logically and stay consistent. In JP, unintended until the sequel trilogy of films, its inaccuracies vis a vis dinosaurs can be attributed to the gaps in DNA filled by other animals, resulting in hybrid animals that aren't true to life but as close as possible.
Thats a plausible logical consequence of the enabling device thats consistent with the real concepts involved.
The opposite of this would just be straight technobabble ala Star Trek, where there might be actual jargon thrown around but its all practically gibberish, with little to no logic and no consistency with any of the real concepts invoked.