He had done interviews with Astorian participants.

Some of those participants had encountered Marie on the Columbia River after the winter.

Some had spoken with her about what had happened.

The book he might have written, if he had included this material, is one of the notable counterfactuals of American historical writing.

The book he did write has been the primary popular source for the Astorian enterprise since its publication.

Its omission of Marie’s survival winter has contributed to the persistent pattern by which her achievement has been known primarily to specialists rather than to a general audience.