Late finish dates are set by the backward pass of the schedule
for the total project late dates 1st it looks for a Project must finish by date then calculates backwards in time from that date taking into the logic and durations and determines the LATEST and activity can finish and start without delaying the project.
it would also look for an activity with finish on or before constraint on it and also calculate backwards in time from that date to determine the late dates
if there is NOT a project must finish by date set or a finish on or before constraint on the last logical activity in the schedule then the late finish date WILL EQUAL THE EARLY FINISH DATE because it has no where else to start to calculate the backward pass
Late Dates are derived from the backward pass starting at the projetc must finish by date
Early dates are derived from the forward pass starting at the date date or the start date of the project
The difference between the early and date date is the total float