Rule 203 (provide means for event ordering) is a must for data change events

[tfrauenstein]

We see event provider teams not consequently following Rule 203 (partially) because they are not aware that it is a MUST rule for data change events and a SHOULD rule for business events. Only very few event types have provided this information, which makes the job hard for change data capture when creating analytical source datasets. We also have seen incidents (e.g. see Post Mortem [internal link]) with the root cause of analytic consumer teams, faced with the absence of this information, made false assumptions on the (business) ordering. As incident mitigation action we agreed to update the rule for more clarity about the must, why, and how and explicitly list the exceptions.

[tfrauenstein]

done with #644