Mike,
It would most likely be because it did not interchange cars or participate in interline revenue divisions with the other railroads.
Also, remember, Alaska was a territory and the ICC was sued by the Alaska Northern to be excluded from the valuation process in 1916. The Supreme Court upheld the Alaska Norther's position. The only source of Alaska, Hawaii and Puerto Rican information is if there was a rate dispute that was important enough to be published in the ICC digest.
Fortunately, I found a grand little bit of information on Puerto Rico in a rate case, but so far nothing in Alaska or Hawaii, except for tha fact that the Hawaiian Railroads were specifically excluded from the ICC Valuation.
Rick