As I understand it about the old Content Creator Source files, it was always a condition and so stated by AURAN for the purchaser of these 2 CDs, if using such content on it, this had to be SUBSTANTIALLY MODIFIED, say by 75% or such to be released again by a content creator as a different content. Also stating in the description of the modified content where the original file(s) came from when uploading/releasing these modified files.
Modifications could mean different textures, different sizes/measurements, shapes etc. of the original files from the 2 CDs, hence it was sort of easy to convert the original files to new content. As far as I know, AURAN (or the Brew Crew) did not enforce rigorously the 75% modification rule, as long as these files were reasonably and substantially modified, all seemed to be OK.
Whether this qualifies others who did not purchase these original Content Creator Source CDs, to also distribute these content source files, be they modified or otherwise, well, you need to ask N3V Games or wait for a better answer here.
Lennard