I now believe, after going through several book lists and biblios., that the 'Third' with '50' on the cover (not title page), 'Revised' with preface by W. K. Hill, was the 1906 edition. I consider the authors, and the Boosey editors, to be honest. The 'airs' obtained are explained in the 1906 (?) preface- Here is the complete Third Ed. preface from the edition with '50' on the cover:

"The demand for a third edition, within a short time after the appearance of the second, has induced the authors to add ten more songs to the previous collection.
"The Authors desire to express their sincere thanks to Miss Laura A. Smith- the talented authoress of "British War Songs, &c., &c., - for her kind permission to use some of the airs from her well-known book, "The Music of the Waters,"* and also to those officers of the Royal Navy and Mercantile marine who have assisted them in obtaining airs of "Chanties" which otherwise they could not have secured."
*THose who wish to study the subject of "Chanties" will find in this book the fullest information."