There are a few psalms in this collection that come from other sources. This is indicated in their headnotes.
There are also some I have written myself. Usually these are where I have felt that none of the examples from traditional metrical psalters quite fulfilled what was required. Some are alternatives for where there is a traditional version which has a tune that might be unfamiliar or difficult to match. This is particularly the case with some of the Songs of Ascent, Pss 120-34, where SH’s version is sometimes in an unusual metre, with an interesting and potentially attractive tune but of which many modern congregations might find difficult to get the measure.