Some useful references from the author of the CogAT himself:
https://faculty.education.uiowa.edu/docs/dlohman/practical-advice.pdf?sfvrsn=2* The Cognitive Abilities Test measures developed abilities, not innate abilities.
* I’m astonished by the number of people who are surprised to learn that they should not use the overall composite score from identifying academically talented children.
* The table below shows that if Level A is administered to every student, errors of measurement remain reasonably small for all students who score below the 90th percentile (emphasis mine). Thereafter, errors increase substantially. [...] Thus, the level of the test that is most appropriate depends on the ability level of the student.
Q: Is CogAT an IQ test? A: No. CogAT measures reasoning abilities. Although these abilities are central to all definitions of intelligence, the word intelligence implies much more.
ETA: In sum: the CogAT under-identifies the highly gifted, who tend who provide unusual answers that are not the single allowed "correct" written response. In addition, because it is a written, group screener with a focus on learned abilities, it also under-identifies 2E, kids working in their non-native language, and kids with less enriched home environments. It can over-identify kids who have had more learning opportunities, especially when used on younger kids.