It might be the difference between shipping from Philadelphia and from Seattle. Or the difference of shipping a new from the builder vs. shipping previously in service locomotives. Or year or two of experience or changes in Skagway.
I understand that BLW had a wharf (or wharves) close to its Eddystone facility. Was the shipment then made by ship from Philadelphia to the West Coast and maybe on one ship all the way to Skagway?
For comparison the San Diego Electric Ry bought some Brill buses built in by J. G. Bill of Philadelphia in the late 1930s and directed that they be sent by ship to San Diego (which would be via Panama Canal). I recall seeing paperwork about this purchase in the collection of Southern California Ry Museum several decades ago.
From Seattle to Skagway was mostly protected water of the Inside Passageway. Also the West Coast operators were probably used to shipping large items to Alaska,
BN