There is a caveat for Alaska.
1) You have to receive the flight training in Alaska
2) You have to reside in Alaska
Then you MUST obtain the night training within 12 months of the certificate being issued - otherwise the Certificate in its entirety becomes invalid for all flying privileges.
See FAR 61.110
Is that because in Alaska, for months on end, it doesn't legally become "night"? So you can defer your night rating until you can find a time and place where it becomes legally "night"?
What was the definition of "night" again for Alaska? Something with the center of the disc being six degrees below the horizon or something?