Thanks for calling this to my attention! I reached out to SkidMarc25 in their personal spriting thread, and this was their response:
Yup they are all free to use and if anyone wants to convert them so they’re compatible with the Repo’s file formatting they are free to do so!
Its just the way I set my files up are not in sync with how the Repo wants them and I’m to lazy/stubborn to change all that myself.