If omitted words are to be found, put each word into it's own line and number it. The same with sentences.
If you are trying to find omitted words and sentences, make one pass with only words, and another one with only sentences. Then combine the results.
Well, let's say that if this benchmark targets AGI, then no help should be given, no segmentation or structuring of information in any way, and it should be able to figure it out by itself.
If this benchmark targets LLMs trained on internet data, statistical engines that is, not AGI, these engines have a preference for structuring of information in order to solve a problem.
Segmenting the problem into smaller parts, using numbers usually, but dashes are acceptable as well, is what they have seen countless of times in textbook examples. When the input doesn't match prior input they have seen, then their performance easily degrades from superhuman to utter confusion. Superhuman for small problems, anyway.
This problem of omitted information is interesting to me, many times I want to interpolate some paragraphs into stories I write, to fill up some plot holes. I used the word "interpolate" in unstructured text, and the results were underwhelming, pretty bad most of the time. From now on, I will number each paragraph, and ask it to find omitted text in there.