I would say it's completely possible even if the internet says it isn't then because they can't hold sperm for over a year. I guess the unthinkable is possible in your tank. As for self fertilization, that is only possible in the guppies as far as I am aware. You never really know, I guess. Your case is very special... you should feel proud of your special fishes.
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Phishie

"An ounce of prevention is worth a pound of cure."