At the end of the manuscript of the Introduction to the second edition, Russell introduces a list of works in mathematical logic with this:
The following are among the more important contributions to mathematical logic since the publication of the first edition of Principia Mathematica.
The list has become an issue of discussion among commentators on the second edition because of what it reveals about Russell's knowledge of logical developments in 1924.
Ray Monk proposes a list of difficulties that Russell faced when beginning to work on a genuinely revised second edition, including this damning charge:
First, Russell had not read most of the recent technical literature on the subject, and had neither the time nor the inclination required to master it.
In 1929 Russell wrote a letter of reference which recommends Leon Chwistek over Alfred Tarski for a position at the University of Lwow. It raises the question of what Russell knew of Tarski's work in 1924. In their biography of Tarski, Feferman & Feferman (2004) endorse the view that it was “Ramsey and others in Russell's circle” who supplied the references for the list.