Reference
OpenAI's Answer
The rights that expired in 1968, causing CBS Records to take over distribution, are related to the legendary soul music label Stax Records.
According to Wikipedia, "During the mid-1970s, a number of factors, including a problematic distribution deal with CBS Records, caused the label to slide into insolvency, resulting in the sale of the company to CBS in 1978." (Source: https://en.wikipedia.org/wiki/Stax_Records)
In 1968, Stax Records' distribution deal with Atlantic Records expired, and CBS Records took over the distribution of Stax's recordings. This change had significant implications for Stax Records, ultimately contributing to the label's financial difficulties and eventual sale to CBS in 1978.
Here's an image of the Stax Records logo:
I hope this answers your question!