Comment by yorwba

To be useful for identifying which model is better, benchmark scores only need to correlate with true performance, for which it's enough that the majority of tasks are scored correctly. You could have a terrible benchmark where 49% of the labels are wrong and a model that always answers correctly gets a score of 51%, but as long as it's higher than the always-wrong model at 49%, it's still directionally correct.

Most machine-learning benchmarks have a fairly large fraction of incorrect labels, but when you just want to distinguish between different models, the time you'd need to ensure perfect scoring would usually be better spent on collecting a larger benchmark dataset, even if it ends up having more errors.