Well, I understand that the bulkhead might be reserved for handicapped. But, in the case of the seat map I posted, someone has one of those blocked seats, but not in the bulk head. How?

I am more interested in how to get them in advance. You can't buy any of these blocked seats in advance. They are never available for sale. I initially assumed that you just can't, but I have been seeing these random blocked seats being taken weeks or months in advance (non-bulkhead) so there must be a way...