1243 discarded (the existing Client has a Session Expiry of 0, or the is new Client is CleanStart 1.

Besides the editorial correction - perhaps it would be simpler to indicate that the Will Message is fired based on the guidelines in <insert reference to appropriate section> rather than repeating the details?

which would be consistent with the language in the next step:

1245 2. The Server MUST perform the processing of CleanStart that is described in section ...