I'm not seeing the mention of two 'order' steps. Are you referring to the larger part of what I quoted?
> MVCC databases may assign two versions: an initial read version, and a final commit version. In this case, we’re mainly focused on the specific point at which the commit version is chosen — the time at which the database claims all reads and writes occurred atomically.
For non-SERIALIZABLE isolation there may be no such "time at which the database claims all reads and writes occurred atomically", which is how I took the rest of the post to mean when running with SERIALIZABLE isolation.
> MVCC databases may assign two versions: an initial read version, and a final commit version. In this case, we’re mainly focused on the specific point at which the commit version is chosen — the time at which the database claims all reads and writes occurred atomically.
For non-SERIALIZABLE isolation there may be no such "time at which the database claims all reads and writes occurred atomically", which is how I took the rest of the post to mean when running with SERIALIZABLE isolation.