I interpreted the original posters point that the git repository could not be modified without destroying it. I thought that's how the next poster was responding to it. If you cannot modify an old entry without destroying the integrity of your system, are you required to modify? Either the answer is yes and you effectively cannot use certain data structures (with their integrity) or the answer is no and certain data structures allow you to keep data.
You would want to avoid using a git-like data structure for data you have to delete. But the example was data that's part of making the copyright license function, and you can keep it for legal purposes.
> But the example was data that's part of making the copyright license function
You entirely missed the point of my hypothetical, which was about immutable data structures like git employs.
As it turns out, our business also uses a git-like hash-chained commit log for our normal database. Deleting old entries would thus violate the integrity of our database. Is that now illegal under the GDPR?