To anyone reading this comment thread - I fucked up the launch and no content was unlocked for the free Itch version of the game.
I assumed commenters were exaggerating when stating that nothing could be used, as my own machine was unlocking content fine.
This was because my personal build was overriding the unlock process and giving me the content, which wouldn't have worked for any other player.
I've explained in more detail in the devlog, but tl:dr I fucked it and a new build is now available which fixes the issue.