What is the date code and other info .......

Safety Float glass produced by the Libbey-Owens-Ford glass company. (LOF)

Libbey-Owens merged with Ford plate glass in 1930. There was an LOF plant in Ottawa.
LOF closed in 1980

Safety Float - early laminated auto glass
AS1 - Windshield
JN - J = May. N= 1971 (so not original)
M23 - Manufacturers code

DOT 15 is Department of Transportation code for LOF company