The twenty-four part circle occurs when the eight part unit circle and the twelve part unit circle are "combined".
Note that the least common multiple of eight and twelve is twenty-four.
Combining the two in this way will result in eight locations along the twenty-four part circle with unknown coordinates.
Note the simple ratio consistancy between circles consisting of different numbers of parts.
Often the eight and twelve part circles are combined and labelled as if the extra missing locations for a twenty-four part circle aren't necessary.
This is a common error.