Livebearer Girardinus metallicus query

-- There has to be somebody out there who knows what I'm talking about. I have other livebearers of the genera Xenotoca, Poeciliopsis, and Limia, and have never noticed anything similar. I will try to take some pictures in the near future to give some visual assistance.

-- Alright, I know there are some knowledgeable livebearer enthusiasts on this cichlid site; I have a question. I have a small group of Girardinus metallicus which I acquired from Rick Borstein - thank you, Rick. I noticed when I first got them that there were a couple of them that were terribly thin. I thought they were, at worst, diseased, at best, bottom of the barrel weaklings I did not want to use as breeding stock. So I culled those two and kept the others, somewhere around nine individuals. The rest were beautiful, healthy specimens and have fared well. They have given birth to the next generation which are growing well and nearing breeding size themselves. However, after giving birth, the large females do not seem to be regaining any size and are reminiscent of those first two skinny individuals. My question then is this: is it possible that the females of this species only spawn once in their lifetime?
-- Before I get any shot in the dark responses, allow me to mention that the females in question are still eating, and living relatively normal lives several months after giving birth, except that they have not regained any mass and look very skinny. I have never seen anything like it and didn't have any luck trying to research the subject. If you've kept these fish before or experienced something akin to this phenomenon, please share your knowledge.