I guess you are right. It _IS_ confusing.
If we assume a certain DC current, there are two ways to reach a desired core operating point:
1. With a given coil, adjust the core air-gap or
2. With a given core air-gap, adjust the number of turns on the coil
The type number LL1660S/18mA is designed such that at 18mA DC current and ALL PRIMARY WINDINGS CONNECTED IN SERIES, the core operating point is 0.9T But if you connect the windings in a different way (such as suggested in "Alt B"), the number of magnetizing turns will be different, and the core will have a different operating point unless you change the DC current.
So for LL1660S/10mA, used in connection "Alt B", the necessary DC current required to reach the operating point 0.9T is 18mA
I hope this is an answer to your question.