Ive actually had a female hold sperm for two years.
Year 1 -
Pastel female bred to spotnose and mojaves = clutch of pastels, mojaves and normals
***spotnose male was sold at the end of this season and I did not have any other spotnose genes at the time
Year 2
Pastel female is bred to a pewter = super pastels, cinnamon, pewters and a sterling
Year 3
Pastel female is bred to a pewter and pastel butter = pewter, pastels, super pastels and a SPOTNOSE (ugh)
That has only happened to me once, but I have to admit Im a bit paranoid with. I only keep visual females when working with recessive genes to avoid issues like this. I know thats not reasonable for everyone, but visual females or virgins are the only way to be 1000000% sure.