Didn't you use something like git / github or other version control system?

Part of why we use such systems is one can thus get diffs between any point in time and any other point in time, see each individually submitted push/commit and so on and so on.

I suggest if you are not using something like git you please start doing so.

Or do you mean a CHANGES file saying in human terms what changes it was that the relevant diffs were intended to accomplish?

(Though each commit has a commit comment in systems like git so again if you submit changes with comments change by change one could in principle maybe even generate CHANGES files to include in distros automatically from the commit comments...)

-MarkM-