Re: Only 57%?
The LD50 value is the experimental result, the percentage that die in the experiment depends on how you search for the value. For example, test 1, dose 10mg, result: 100% survival; test 2, dose 20mg, result: 90% survival; test 3, dose 40mg result: 30% survival, test 4, dose 30mg, result: 50% survival. Over the 4 tests, the experiment has killed 32.5% of the animals. Another experiment on a different substance could have a much higher lethality. 57% is an average over many experiments, so maybe the experimenters are, on average, fairly good at predicting the toxicity of a substance.
But, you miss my point. Part of the procedure is, something like, 'at the end of the experiment, dispose of the consumables according to standard safety procedures and clean the lab', where 'consumables' includes lab rats, and the standard safety procedure is kill and incinerate. None of the animals leave the lab alive, even if they survived the dose.
On your big question, I would hope that the reviewers at Toxicological Sciences would reject a paper that only 'predicted' the training data, but it would be nice to see confirmation.