That was my plan B – the problem is it is a workflow issue as it is a complex system and could result in many content types so the admin would need to go into 6+ content types and create items to create what they want so attempting to minimise.
I had an alternative I am testing where I add one of the fields for the repeater sub-location as a taxonomy and have that serve as an ID for the sub location. I would then be able to select that taxonomy item from the other custom post type and know which of the sublocations was required. However, even if “create new items” is ticked for the taxonomy field there is no way to create new terms on the fly as the field options are only select/radio/checkboxes.
I will sleep on it but I think I will admit defeat and go for @rumo suggestion and just make a new custom post type.
