Duckworth’s New Readers Library series was initiated in 1927 and the majority of titles were published by 1931. The highest number in the series (from WorldCat) is Twelve Modern Plays, selected by J. Hampden published in 1938 as #66 in the series. Titles are reprinted until 1946.
An earlier Duckworth series, with at least 50 titles, was called the Reader’s Library, published from 1810-1927. It underwent significant revision in content and format (including the size of the book) when the New Readers Library was issued in 1927.
A Duckworth catalog, detailing their series and libraries, was included in the back of the Readers’ Library edition of Hudson’s El Ombú published in 1920. The entire catalog is here (PDF). Series listed include:
The Crown Library (8vo., 7d/6s)
Modern Plays (3s.)
The Reader’s Library (Cr. 8vo., 5s.)
The Roadmender Series (Fcap. 8vo., 3s./6d.)
Two Shilling Net Series (Cr. 8vo., 2s., paperback)
The Student Series (Cr. 8vo., 2s., paperback)
New Readers Library titles were printed in a smaller format (12vo.) than the earlier Readers’ Library (8vo.). The copy below is the first title in the series, published in 1927. A red paper jacket with no decorations includes the series name (on the spine and jacket front) as well as a summary of the title. Price (clipped here, but 3s./6p.) is on the front flap.
An advertisement for the series is on the back flap and list of titles on the back of the jacket. The series had reached 20 titles at the time of this books publication, the first year for the series (1927).
Bindings are of blue cloth with gold stamping.
Series titles are listed facing the title page.
Two more titles from the series, Green Mansions (1929, third printing in the series, first 1927) and After London (first printing in the series, 1929).
The 1929 printing has the longest list of titles, with 44 on the back and numbers 45-50 on the front jacket flap (below).
It seems that few new titles were added in the series after the mid 1930s. Some reprints have dates up to 1946.