Not necessarily. It depends on how sunlight is shining through the glass. The old M400s that were in use in Lewiston and along the Robert Moses Parkway were pre-1962 fixtures.
Was it mounted to the bridge or on a standalone pole? If it was mounted to the bridge it's likely the age of the brige. When you drive over a bridge there's generally a plaque with the year the bridge was built either at the begining or end on that concrete endcap where the green, red, silver, etc guardrail starts. that age can hint to the age of this light.
And tpirman a suggestion, don't note fixtures such as "1959 GE M400" like that because the silver M400 came with different characteristics as the years progressed. For example, there were silver M-400s with grey gasketing, and silver M-400s with thumb tabs molded into the door release. Same thing with the OV-25. I use something like "First Generation Westinghouse OV-25" for example. Because there are minute things that can differentiate fixtures.