Seasonal affective disorder - if you have it in the winter, and then it continues into summer, do you change your diagnosis?

Yes. Seasonal affective disorder should improve as the days get longer. If the mood symptoms persist into the summer, it's more likely a person has major depressive disorder or dysthymia. It's important to see a health care provider for the correct diagnosis in case treatment would help.
SAD. SAD is now referred to as Depressive Disorder with Seasonal Pattern in DSM 5. It is a subtype of depression. SAD usually occurs in fall & winter for most people. However, there are some people who experience it in late spring and summer. I don't know of any other patterns with SAD. Would reassess.