Guppy having premature fry

On August 21st I purchased a male and two female guppies to learn to bread them. On the 22nd one was giving birth and on the 24th the other female was giving birth. Since I wasn’t expecting them to give birth so soon I had to move them around but ended up with 18 healthy fry. As of today all are still growing strong and doing well.
This evening while doing maintenance on the parents tank I noticed another fry. This one must have been born today because he was extremely small and I had not noticed him earlier today. My question is it possible for one of the females to give birth to a single fry 10-12 days later. If so would it be a premature fry from the next pregnancy or the previous pregnancy. If it is from the previous pregnancy would the clock start from today or when she had the majority of the fry?