Which hymnal is abbreviated NPM?
No idea. Where did you find the abbreviation being used?
It appears in each of the Lectionary Hymn selections for May 2020:
Related to John 10 (National Association of Pastoral Musicians (NPM))
Is there an index of the abbreviations used in this context? Also, is there any information about why NPM leaves the A out of their abbreviated name? Are NPM and LUYH the "names" of particular Hymnary editors? (The page CalebAndCo pointed seems to make that assertion.) BTW "Abundant Life" is a fine text that I hadn't seen before, so thank you both for leading me to it.
Hymns with "NPM" were recommended by the National Association of Pastoral Musicians and hymns with "LUYH" were recommended by the editors of the "Lift Up Your Hearts" hymnal.