I used my miles to book an SQ award ticket for my father recently, and it gave me a chance to see the blocking in action. When my dad logs in with his eticket info to select a seat, there is nothing available before row 40. When I check his reservation via my account, the 30s rows have quite a number of available seats. But when I try to select that forward seat I get a message that this ticket does not allow me to select those seats. I am still stuck picking something in the 40s.