Those fish 2 or 3 months apart... from the same source... you don't think they are from the same parents? or from the offspring of the same parents?I often see people make this mistake with livebearers. People go to the LFS and select some males and females of the same strain, not keeping in mind, that all the fish in that tank are probably siblings.
Having made that mistake myself with a few fish, I have to admit that deformities were as high as 25% in their offspring. We are talking very good looking fish here (show quality if you wish, with all the horrible things people do to produce those fish).Now I make sure to get fish 2 or 3 months apart if I want a pair.