Based on the content size, it appears that we have one significantly smaller file, likely to be the README.txt, and two larger ones, possibly JSON files related to annotations. I'll start by investigating the smaller file, assuming it to be the README.txt, to identify any missing documentation details about specific files, as hinted.

Let's open and read the presumably README file first to check its content.The README file includes details about the dataset "TumorSegmentation", its export date, the number of images, annotations format, pre-processing applied, and the provider/license information. There's no direct mention about specific files such as annotations data or lists of file names included in the dataset. Assuming that the other two files are related to annotations as per their likely JSON format and given names, it seems there might be an issue with missing documentation details regarding these annotation files.

Let’s document this issue for further investigation or correction.

**Issue 1:**

- **issue**: "Missing documentation details in README"
- **evidence**: "Tumors are annotated in COCO Segmentation format."
- **description**: "The README mentions that tumors are annotated in COCO Segmentation format but does not specify the names or details about the annotation files (_annotations.coco.train.json, _annotations.coco.valid.json) that are included in the dataset. Including file-specific documentation is crucial for understanding and using the dataset correctly."

This concludes the first issue identified in relation to the provided hint. Next steps would involve verifying the content of the large files to understand their structure and relevance to this issue further, although the initial task is focused on identifying issues directly from the README.txt content.