I recently purchased my first Longines, a Longines waffle dial 10k gold filled automatic, 34mm, 40mm lug to lug, 12.5mm thick, 18mm strap size with an in-house 19AS automatic movement. I wrote to Longines and they gave me the following information:
"Originally, the serial number 10'471'624 identifies a Longines mechanical self-winding movement, caliber 19AS. It was invoiced on 16 July 1958 to the company Longines Wittnauer Watch Co., INC., which was at that time our agent for the USA. The other parts of the watch were produced locally under license from Longines. Unfortunately, since the relevant archives are not in our possession, we are unable to provide any further information on your model."