Fun fact: There's a cheat code that lets you unlock PT Ultimate for all files, right from the title screen!
Here's how you do it:
Boot up the game to the title screen. DO NOT PRESS ZL + ZR.
Hold R and + until you hear a ping.
Press UP, DOWN, LEFT, RIGHT, X, B, Y, A
If you did it right, you'll get a jingle and a popup.
Have fun dying in File 01 :)
And for all those "it's Astral Chain's FINAL SECRET!" people out there... it's probably not. The buttons on the D-Pad don't make a "P" symbol (the platinum code is actually ↑ ↓ ↑ → ← X B Y A). There is actually one more place in the game's code that plays the Platinum Command sound effect (core_GUI_Platinum_Command), but I've never gotten it to trigger. Perhaps Astral Chain's final secret is still waiting to be found...