[adrian_b]

OK, you may be right.

I have always verified that rsync copies the modification timestamps with nanosecond resolution, because I use these timestamps, but I have never looked at the creation times, because I do not use them.

I always have content hashes attached to files in an extended attribute.

For detecting duplicates with different names I always use the content hash, which is much more reliable than a creation timestamp and it is also useful for other purposes, e.g. for detecting file corruption.