Gary (Refined Reflections) is really the expert on paint, he used to own paint shops for many years. Different paints will hve different characteristics when cured, ie. some harder than others. My understanding is that will be down to both the make up of the paint, and if it was oven baked or not.
A 4 year old Porsche I did last week was a nightmare. It lives on the road in the centre of London, and gets knocked/keyed on a very regular basis. The whole car has seen paint at various times, work carried out by different bodyshops. In places, the paint was so rock hard I could barely make an impression on it. In other places, it was so soft a finishing polish was all that was needed to remove 100% of the defects. It made for a very long difficult day because pretty much every panel has to be treated as an unknown.
A detailer will know if a panel has been resprayed or not (but its always nice when someone tells you), my point was that if you get the car detailed a short time after the work has been done, what products we use will depend on the process the paint has been through. Paint that isn't fully baked/cured before it leaves the bodyshop needs to 'breathe', solvents in the paint escaping to allow it to cure. If you were to put a sealant over that new paint which prevents the solvents escaping, there could well be problems.