Commander X16

I'm specifically referring to the files here: https://github.com/commanderx16/x16-demo/tree/af282c208c89400b64a977de91e31ec7031b2807/assembly

I was using the mode7-bitmap.bin and mode7-palette.bin files for a project, and I'm looking to upload the demo here. Everything else in the project is licensed under the BSD license (mostly 2-clause, but one source referenced was 3-clause, so I'm including both), but I can't find any license for these projects specifically. The only reference to licenses is in the CONTRIBUTING file where it states submitted demos needs LICENSE information in the source files, but there are no such comments in the mode4/mode7 assembly files. Looking at the Git history, I can see the demo was uploaded by Michael "mist64" Steil. Is there an official license the demo would have been released under?

On a related tangent, I would like some advice/clarification as to who to credit for some of these things. The mode7 demo image is of "The 8-Bit Guy", so I assume he holds the copyright on the original image, but I assume "mist64" converted it to 8bpp. I was planning on naming both as the credits for the image file, but is there something different I should do? Similarly, I'm not sure how to credit this file in the ROM project. The README states that "All new code, and additions to legacy code" are copyright "mist64" and licensed as BSD 2-clause. However, walking through the Git history (including through file renames) shows that the original file is (almost) entirely submitted by Frank van den Hoef. Who is the proper person to credit in this case? I also assume it's licensed under the BSD 2-clause license due to the README, though older versions of (basically) the same file, such as this one, state it's "License: Public Domain." I would appreciate clarification on this if possible as well.