Postseason achievements are not counted by MLB in players' career statistics, which are an accumulation of performance numbers during regular-season play. However, players do have career postseason statistics kept, only separate from the regular career numbers.

Do postseason stats count NFL?

Nope. Though they do keep all playoff stats as a separate thing that you can look up and compare.

Do NBA playin stats count?

Just a reminder: Play in stats don't count towards anything.