Prior to their rediscovery, it was believed that Coelacanth were one of the first aquatic creatures that experimented with walking.
And when you look at the claims you find they have merit. Coelacanths were part of the lobed finned fish group which were supposed to have used their fins for ground locomotion. We have the benefit of 70 years of science and discovery since then, and we are reasonably sure that Coelacanths didn't do this, but the fossil Coelacanths were closely related to other similar fish that did.
But as we unambiguously know now, that's a complete fabrication spawned from little more than guesswork.
We do not know this - even ambiguously. It wasn't a complete fabrication, it was based on evidence.
If the Coelacanth were never rediscovered, this kind of imaginative "fact" would have gone on unchecked and you'd be none the wiser.
Possibly, or possibly not. Nowadays we rarely state that a certain fossil was a direct ancestor of an extant species, if ever. The claim would have ultimately been, "Devonian fish, like the Coelacanth, could have used their lobe fins in a fashion we'd expect from the ancestors of modern tetrapods".
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