Although I was brought up on the 1951 Hymn Book and then the 1973 edition, I have never previously seen this supplement.
All of these tunes were quickly absorbed into the 1954 Little Flock Tune Book (blue cover) and (where known) the year of birth and death as well as the composer's name is shown.
For composers who were still alive at the time the book was compiled, it would appear that the only date given was the date the tune was composed.
There are 530 tunes in that book, and a further 297 in the later (1965) Supplement (burgundy/carmine/maroon cover).
Sadly these two books only include the tunes (no words), but we also have the 1932 edition (words and tunes).
Steve
P.S. While on the subject of Hymns, does anyone have suitable sung recordings (which could be included on this site) for the two missing from Spiritual Songs 1978 - 198 & 324?