About Validation Rule Checks

After defining validation rules for a model, in a story based on this model, planners can only enter data for the valid dimension member combinations specified in the validation rule.

If the planning users add all the dimensions that are defined in at least one of the rules to the table, all invalid data that couldn't pass the validation rules will be marked with validation warnings. Parent-level data will be marked as invalid only if all the base-cell data are invalid. Unbooked cells that are invalid are disabled for data entry. For more information, see About Validation Warnings.

If the planning users disaggregate the values in such a story, booked data have higher priority than unbooked data:

If the planning users disaggregate a value to both valid and invalid booked data, the value will only be disaggregated to the valid booked cells.
If the planning users disaggregate a value to both valid and invalid unbooked data, the value will only be disaggregated to the valid unbooked cells.
If the planning users disaggregate a value to invalid booked data and valid unbooked data, the value will be disaggregated to the booked invalid cells and an error message will inform the users that the disaggregation failed.