There will be a good number of players who will hit free agency in March because their contract is up. But the full list of available players will change before and after the start of free agency because of what are most often referred to as ‘cap casualties’. Which basically just means players who teams think are paid more than they are worth or more than they can afford and they need to get them off the books before guarantees kick in.
Therefore any lists of free agents won’t entirely include many of the best players who will be available.