On my window sticker it states "Assembly Point/Port of Entry:Mexico City, Mexico". Maybe it has something to do with how the trucks are shipped out ( by boat through the gulf or by railroad ) ? I thought that mine was going to be sent by boat and into the port in New Orleans or the Port of Pensacola in Florida but it was sent out by CSX Rail Road to Lawrenceville, Georgia and than shipped by truck to Florida.
If the Lago Alberto plant and the Mexico City plant are the same maybe it is the method of shipping that determines what is on the sticker.
Also, it seems to me that all the Lago Alberto trucks and the Mexico City trucks are getting the undercoat or sealant and the Saltilo and Missouri/Dodge City trucks don't. If the two (Lago/Mexico City) are one and the same that would explain why they both do the undercoat treatment. Just my $. 02 worth.