the only Y seats on Copa flights that are blocked off are the first 3 rows (5,6,7), which Copa Elites can choose at booking.

Exit rows are nearly always available whenever I book flights. Most Copa flyers I guess would never do online checkin or change their seats. A ton of people buy their tickets from the Copa desks/shops around Panama, who just assign them seats from 8 back, skip exit rows and then 22 back (737-800s).