What Alfred Russel Wallace Really Thought About Darwin

The metadata for some random entry I clicked on reads like:

LETTER (WCP1.1)

A typical letter handwritten by author in English.

Held by: Natural History Museum
Finding number: NHM WP1/1/1
Copyright owner: Copyright of the A. R. Wallace Literary Estate
Record scrutiny: 01/12/2011 - Catchpole, Caroline;

I'm curious about the copyright field. Aren't the letters supposed to be public domain? Since Wallaced died in 1913, which is well past the 50-75 years after death clause of most countries' copyright regimes, shouldn't the copyright on the letters have lapsed already?

IANAL but I'm assuming that the letters have already been "published" by virtue of their having been snail-mailed and read by a second party. It's not as if they're some long-lost manuscript that's been hidden in some author's dusty drawer, which can arguably be considered as unpublished.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/fg7QoNwcrq0/story01.htm

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