Aspan

Slightly confused here.
MIA-YYZ-YVR on Thurs.
Booked on Lat flight pass with confirmed SWU cert upgrade.
Arrive for flight and MIA-YYZ is delayed due to plane change on the outbound from YYZ.
45 min delay 10:30 now 11:15.
Check in, ask about tight connection and I am told "if you don't make the 3:00 to YVR, you are protected on the 4:00"
Okay fine, hand the the cert, receive BPs, note on file have carry on only and cert taken.
Only half full J cabin MIA-YYZ
Get the gate in YYZ, plane is just pushing out 5 min EARLY. "Sorry sir, we could not wait, I can put you on the 4 in Y or the 6 in J. I thought was protected on the 4 due to the metal problem. Sorry sir J is full but I will waitlist you." Get new BP and head to new gate.
Boarding begins and wait to see if the upgrade clears.
Gentleman approaches GA and says he is on the 6 but what about the 4. Same routine y yes j full.
I am told no upgrade and proceed to 14C.
Halfway thru the flight I use the washroom and see the other pax in J. Hey lucky him.
A couple of questions:
1. The MIA GA should have been able to check the J status of the 4 to YVR so why tell me I am protected. The flight from MIA is short and usually XMed. YYZ-YVR is much longer and can be old equipment. Knowing this I would not burn a cert for a 3+ hr flight only.
2. How does AC decide on U/Gs ? The other pax ends up on an early flight in J and I am on the later flight due to AC not leaving on time and stuck in Y and no IFE to boot.