Mike...
...One thing that can happen to dodger windows clear vinyl) is that mold can grow inside the plastic. Many times you will see dodgers that have lost their clarity and look like they are sunburned with blotches. This is mold. Once there, there's nothing you can do for it except replace the glass. Keep an eye on it because it will spread.As far as it happenning over the winter, it was probably stored in a cool, dark place that enhances mold growth.To prevent this problem on new dodger glass is to use a good quality vinyl cleaner that will restore the oils to the vinyl and apply a couple of times a season. I have a favorite brand that I use and have had the same glass for 9 or 10 years.