What do we list for the year when the range of dates is known but not the particular year. For example, a vehicle was made 1980-1985 but the particular year can't be identified. Do we use first year, last year, just pick one or just leave it blank?

Usually we use the first year of the possible range, and indicate the range in the comments.
In some cases we can take the highest year, e.g. with an obviously brand new car it could get the same year than the movie.