This book was described in the bibliography of 'A Most Ingenious Paradox, the art of Gilbert and Sullivan' by Gayden Wren, entertainment editor for the New York Times as "An indispensable reference source. Allen has done admirable research, both in the D'Oyly Carte files and in apparently every review of any Gilbert & Sullivan first night ever published."
Later, Gayden states "...Allen's text stands as a unique and valuable reference, and can be recommended to anyone who can find a copy - especially if it still has the facsimiles of the original programs, included in the same slipcover in the original package".
I believe this accurately describes the book I purchased.