That would makes sense to me if the additional non-PI column did not make any demographic changes, like all rows had the same status value and multi-column stats were on PI+Status.
I excluded the PI ones because I would not expect to see that situation often, for this particular reason.
Sometimes you will see PI+Partition, or PI+Partitioning columns. These do provide some specific information to the optimizer in some Teradata versions
I don not personally know the reason for this, but this is the way things work. For instance if you concatenate a few fields and one of them is NULL the result is also NULL.
This seems consistent with the multi-column stats rules