I was so frustrated with this same question that I spent some time researching and finally have an ANSWER. The answer is from Wiley text books and FASB ASC. The problem is that multiple sources call the same thing differently.
What is commonly known as Cost Method (ASC 325-20) is <b>NOT</b> the same thing as what Wiley calls Cost Adjusted for Fair Value Method. Repeat, It is NOT the same. What Wiley is referring to, might be known to you as Marketable Fair Value Method, or Adjusted Fair Value Method or simply as Fair Value Method for (AVS) available for sale or (HFT) held for trading investments(ASC 320).
In Rogers and Becker reviews, you learn about both 1. the Cost Method for hard to determine fair values of investments (ASC 325-20) and 2. the Marketable Fair Value Methods (ASC 320). Both of these are appropriate for 0% -20% ownership.
When Wiley refers to Cost Adjusted Fair Value it just means the methods for HFT and AVS securities, which are not the same as the Cost Method. The Cost Method does not record unrealized gains/losses while the Cost Adjusted Fair Value does. Basically, you learned this in your CPA review course but Wiley just calls it differently.
References:
https://accountinginfo.com/financial-accounting-standards/asc-300/320-investment-securities.htm
https://accountinginfo.com/financial-accounting-standards/asc-300/325-20-cost-method.htm
tl;dr: You learned about Cost Method (ASC 325 )and Marketable Securities Methods(ASC 320), Cost Adjusted for Fair Value Method is referring to the latter of the two for AVS and HFT securities.
.