I think your original model was correct, and I would not make Richard’s change. The After indicates that everything stratigraphically later than this sample dates after it, but it has no known chronological relationship to stratigraphically earlier events. In your model, the only earlier event is the Boundary Start. However, Constraint can indirectly affect Start and the Phase D dates as it modifies the distributions for samples in Phase E, and these are used in calculating Start. This is what you were seeing initially. Your model is saying that a priori you do not know how Start is related to Constraint.
If I run your model with all the C14 dates shifted 100 years later, it is clear that Start is not required to be earlier than Constraint.
In the model without After, Start is forced to predate Constraint. I suspect this is not what you want your model to do.
Dr. Andrew Millard
Associate Professor of Archaeology,
Durham University, UK
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