I propose to put the changelogs for the current master in the final location, e.g. now starting release: 10.4.
The file location will influence the URL. If these are changed, all already generated URLs (which are often linked and indexed in search engines) will be broken.
I know this is documented differently:
New changelog files should usually be added to the
typo3/sysext/core/Documentation/Changelog/masterdirectory. If a version is to be released, all files in this directory will be moved to a directory that is named after the release number.
The URLs that are generated in master are now all broken. These have already been indexed in the search engines, linked from decisions and other places.
I see no disadvantages in changing this.