Mark0n very good question! Similar situations already has occurred. In such case if for instance, Croatia/Slovenia would promote, the spot would be reserved for the country which player gained more points at that season (including difference in keeping points between A and B group). So in your example, if Croatian player gained more points than Slovenian one, Croatia 2 would promote, if there is no second Croatian team, the spot would be used by the next Mixed team. Next Mixed team is also formed on rating basis, so possible would not comprise of neither Croatian nor Slovenian player. Nations league format is complicated to manage , so I do not describe all edge cases in tournament description.
