Mike says to Pat that only one person was executed in the United States last year, and this is true. Seeing this was released in April of 1983, it must have been filmed in 1982, so Mike was referring to the calendar year of 1981, during which there was only one execution, that of Indiana quadruple murderer Steven Judy in March, 1981.
From this film, Stacey Keach, Don Stroud and Kent Williams were the only regulars of the television series run on CBS for it's five seasons as well as appearing in the second Mike Hammer film in 1984, More Than Murder, which led CBS to greenlight a complete series.
Mike drives a 1970s Blue Ford Mustang for part of the film and the rest of the time, he's either walking around Manhattan or given a ride by someone including Captain Chambers.
Filmed in late 1981 early 1982 with the intentions of turning it into a regular series if it was successful as a movie of the week for CBS which it was which gave it another movie of the week filmed in 1983 called "More Than Murder" which guaranteed that Mike Hammer would be a regular series starting in 1984.
The New York Scenes were filmed during the Winter of 1982 as you could see by the amount of snow visible for those scenes and the rest shot in Culver City including the second half of the car accident which clearly has no snow and the background is Los Angeles.