The file pricing system works on a tier basis.
Unlike when you buy a game on Itch, where you buy ownership of the project. When you use the file pricing system, the person does NOT buy the file, but pays X value.
If a file costs X, anyone who paid X or more can access that file. Note that the only rule is the value of the file.
If you add a file that costs X, it doesn't matter if the person paid a year ago, or tomorrow, if they paid X or more, they can access that file.
If you have a file that costs X, and a person paid X, they can access that file, you now change the value to X+1.
That person LOSES access to the file, and what's worse, they can't just pay the difference, but must pay X+1 again to be able to download that file again.
The system is good if you want to incentivize someone to pay or donate more than the minimum value, by offering additional content.
But it is very bad if you want to sell a file, especially if you are going to change the value of that file in the future.