Nope they were not all built there.
My GTX was built in Windsor as well and my broadcast sheet was under the rear seat until I misplaced it.
According to Alaskan_TA's site:
Here are some places to look:
* Taped to the back side / top of the glove box insert.
* Under the front bucket seats in the springs
* Inside the bucket seat backs
* Under the rear seat bottom
* In the rear seat back.
* Under the package tray(speaker shelf)
* Under the carpet
I don't know if it applies to all factories but sometimes it doesnt hurt to check.