These represent the software build number. Not every build is released publicly, so you can infer from this that quite a few changes were made since the last release.
You can see the changes in the release notes.
Hi all,
Today we are releasing a major update to the way in which Roon determines which versions of streaming content to display and playback.
Roon makes it easy to navigate across tens of millions of albums and tracks, even when multiple versions of the same album are available – the Versions tab lets you browse different formats and sources, across multiple streaming services and your library.
If you have multiple versions of an album inside your library, you can select a “primary version” …
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