Are the OSM boundaries, or the Google boundaries more correct (presumably OSM is just the NP, Google the Preserve too?) - if Googles, then I concur, if OSM then there's a lot outside the national parks.
The
National Park Service's map for Wrangell-St. Elias differentiates between the park and the preserve. OSM's boundaries more or less follow the "park" boundaries, while Google's lump together the "park" and "preserve" parts. NPS boundary signs along the McCarthy Road also distinguish between the park and the preserve, indicating whether the park is on both sides of the highway, or the preserve is, or in some places the park is on one side of the road and the preserve is on the other side. (I don't know about the Nabesna Road, since neither I nor GMSV have been there, though the Milepost travel guide suggests that its NPS signage is similar.) Those signs are most relevant to hunters/fishermen/trappers, since they are under looser restrictions in the preserve than in the park.
But on either side of the line,
the land is protected by the NPS, and there's not much difference between park and preserve protections. And the major tourist destinations within Wrangell-St. Elias, especially the historic Kennecott copper mine and the nearby small town of McCarthy, are within preserve rather than park boundaries. So I would lump together the park and the preserve.
The park/preserve distinction doesn't come up that often. There are only 21 national preserves in the U.S., 10 of which are in Alaska. Of the 21 national preserves in the U.S., 11 are combination national park (or monument)/national preserves. Seven of them are in Alaska, and of those only two (Wrangell-St. Elias, Denali) have roads in their park areas, and two (Wrangell-St. Elias, and the isolated Katmai in southwestern Alaska) have roads in their preserve areas.
FWIW, the Generals Highway, in California and usanp, starts in Kings Canyon NP and ends in Sequoia NP, and is a key shortcut between the two parks. But the middle of the highway is in Forest Service lands (under the U.S. Dept. of Agriculture), rather than NPS (Dept. of the Interior).