Stefanie, it’s difficult to compare the three fish since on the photos they are not to be seen equally perfect and from the same angle and pespective. I am unable to say that they are different concerning the pointedness of the dorsal fin or some markings in the one but not in the other individual. You could observe all this by no means better in front of your tank than we seeing these pictures. There are differences to be seen, but they lie within the range of individual divergence of a single species, I should say.
However, it is clear that the pictures show very well developed females with the potential to spawn, and it is a pity that they have no male(s) to do so. The blackish spot that you speak of and that is, according to your words, better to be seen in one individual only, is by no means an indication of P. sumatranus, as one could think (you did not indicate that), since it is much more prominent in that species (or even in allani), whereas the body structure is clearly different, especially in sumatranus. The short filament (= ca. 1 mm) at the end of the sumatranus-caudal is missing, too.
The fine pictures again illustrate that we are nearly unable to distinguish between the females of many Parosphromenus-species that are close to bintan, say e.g. spec. “blue line”, spec. Sentang, spec. Dabo, spec. Dua, but also alfredi, rubrimontis, harveyi or opallios, even female of nagyi of the variant from Cherating or Cukai or Pekan Nenasi (not the classical form of the first description from Kuantan!). It is very likely that they belog to that variant that was imported at that time when you received them. On the other hand we are (if experienced!) are sometimes able to recognize females of species that are more or less near to the bintan-type, as e.g. filamentosus, phoenicurusor tweediei, and the true deissneri.
If you still remember or have a description of that situation and if you still have male form that import, I should try toy pair one of the females with one of that males. We really don’t know how males react to females of not exactly their own species or form, but a close relative. Without exact genetic information, we have nearly no information about the measure of closeness or distance that plays a role there. So we don’t encourage people to mix potentially different animals clearly. But in your case it might be justified to try it if you have males that may stem from that import and if you are able to do a controlled experiment in a separate tank and we could see whether it works at all or not. And then we can discuss the outcome. Without that we cannot be sure about anything. Having done that maybe we can’t either, but we have more information. It could be that we can presume it’s species xy, or not.
So, have a controlled try, if you can.