I asked the same thing about a Joey Votto card not too long ago. I believe the response was that a player’s “official” rookie card is the player’s first card from a major set release. I’ll edit if that’s incorrect or slightly incorrect - someone please correct me if so. I also think there might be something in the FAQ about RC tags.
Greg Maddux, Ronald Acuna Jr., Jacob DeGrom, Max Meyer, Noble Meyer, Kemp Alderman, Spencer Steer, Cole Caufield, Cale Makar, Josh Norris, Pokemon, A&G mini sets, oddball and art cards
Almost everything in my main collection is FT/FS even if it is not listed in my traders!