I've had several of my snakes attempt litters of stored sperm. I currently have a Florida blue that has decided to try again so to speak. Last year I had my big parietalis produce a stillborn amongst a collection of 'slugs' a year after being mated.
I know others who have commented on owning garters and regularily getting two litters a year.
In the wild it's more difficult to prove due to the chance of meeting a mate as well as not knowing if the 'late' litter was actually simply due to the female not reaching prime condition until later in the year - but has been hinted at in some studies.