playoffs don't count
playoff games are not a factor in Calder eligibility.
in your example, Ladd is no longer eligible this year for the Calder because he played 26+ games in the regular season. (I was not happy when Ladd played his 26th game because I have him in a salary cap based hockey pool where you can keep Calder-eligible rookies without them counting against your cap)
The definition of "prospect" on this site has nothing to do with Calder eligibility just in case you didn't know that.