It's different than the standard husband, wife, two kids, white picket fence scenario, highlighting how blended families introduce unique legal challenges not commonly addressed.
The decrease in this February's mean represents a change in population and a change in overall performance. In four of the past five years, the MBE mean for California has been higher than the mean for the combined non-California jurisdictions, so it makes sense that removing California from the national pool might bring the national mean down slightly.