Hybrids are hybrids, species are species. A liger is neither a lion or a tiger. Mikawa JBP are P.thunbergii pines in the area that used to be called Mikawa Province. There is genetic diversity in any species and Japan is a thing stretched out country of many islands. But even for the biggest expert telling is an individual pine is a Mikawa kuromatsu or something else is always still guesswork.
Kotobuki black pines are clones of a certain bud mutation. It is a special cultivar of P.thunbergii. If Kotobuki was a bud mutation of a Mikawa JBP then all tree are JBP or P.thunbergii. All Mikawa pines are P.thunbergii and all Kotobuki are Mikawa pines.
This is also how you get dwarf forms. They are not species but cultivar of certain species. They may be found in the wild or not, but almost always they have no future there. That's also why all those dwarf forms of mugo pine and all those odd looking versions of irohamomiji are grafted on their ordinary species rootstock.
The only reason why there are millions individuals of the 'Mops' version of P.mugo is that someone saw this bud mutation and propagated it. Without humans right now we would have 0 'Mops'. It would probably be extinct.
Broccoli, cauliflower, brussel sprouts, cabbage, Chinese kale, ordinary kale, red cabbage, collard greens are all forms of Brassica oleracea species. None are hybrids. All are cultivated by humans from certain different species populations. Yet they are all different.
Durum wheat is called Triticum durum but originally a tetraploid hybrid of Triticum urartu and Aegilops speltoides. Triticum durum is not Triticum urartu.
'Sir Robert' is thus not R.indicum. All it's parents are hybrids and none of them look like the R.indicum species as it is found in the wild. Rather, the whole lineage looks a lot more like R.tamurae (old name R.eriocarpum). It looks more like 'Kaho' than like 'Kinsai'.
But in fact the Japanese call all azalea of western origin 'azarea' or 西洋ツツジ no matter how they look or what their parents are. They don't mean to disrespect and this isn't really a conscious decision on their part. But satsuki is their word and they apply it to their azalea.
What we do in the west often doesn't fit their categories and they don't feel like changing it in the same way they don't feel like using western botanical names for their own traditional plants.
In a same manner we don't call the most boring and mundane version of R.indicum found somewhere on a mountain 'satsuki'. To us satsuki are those stunning flowers we see on azalea bonsai. And R.indicum is that humble flowering scrub that grows in the Japanese mountains and that generally only western botanists care about.
But to the Japanese both are 'satsuki' since they don't have the word R.indicum. But really no one grows R.indicum in Japan. They all grow their cultivated azalea. They do grow their split petal forms or R.indicum, their rose petal forms of R.indicum, their tetraploid versions of R.indicum. This would be analogous to Kotobuki JBP and P.Thunbergii. But satsuki that appear to be special forms of R.indicum (we don't know for sure until someone analyses the genes in a laboratorium) make up only a very tiny amount. Most satsuki don't look anything like R.indicum, R.tamurae or even their natural hybrids.
We grow a lot of tulip and daffodil here in the Netherlands. That's what we are famous for. But Narcissus pseudonarcissus or Tulipa gesneriana, you will be hardpressed to find those anywhere outside of botanical gardens or labs.