The VIN plate was attached to the a-pillar from 64 through 67 and moved to the top of the dash in 68 so it could be seen by LEO through the windshield.
Different plants used different formats throughout the years on VIN plates. Why? Only the plant SOP would know. Since you're asking about Atlanta specifically in 1965, the format is the 6-digit division/series/model/year, followed by a blank space, the plant letter "A" and another blank space then the sequence number such as:
138375 A 123456 - See http://chevellestuff.net/1965/vin_samples.htm
for some 1965 examples.
In 1965 Baltimore and Kansas City strung all 13 alphanumeric characters in one contiguous sequence such as 138375B123456 or 138375K123456.
Framingham was the same as Atlanta, such as 138375 G 123456.
Fremont was different yet. It appears that Fremont prestamped the division/series/model and when it came time to stamp the entire VIN would then add 5Z123456 making the plate look a bit odd. Often the two individual stampings were not aligned as this El Camino shows.
As for other years, there are just too many differences between years and plants to describe them all here. On my website at http://chevellestuff.net
there are menu links for 1964 through 1972 with individual year links titled "Vehicle Identification Number (VIN) Plate Breakdown and each of those pages describes how to read a VIN plus a link to pages with examples for that year.