I had a similar experience on a DCA-JFK-LAX trip a few weeks ago. No problems with the upgrade for the 42 minute trip from DCA to JFK, but 0 seats in J (a flat bed BE cabin 767) on the JFK-LAX route at 3 hours before departure. Then, 90 minutes or so out, 3 J seats opened up (I was #3 on the UG list); during boarding, a 4th J seat opened up. Happy happy joy joy!!!