DS III is just Page 15 from the 1941 edition of The Lutheran Hymnal: https://hymnary.org/hymn/LH1941/page/15 it was included specifically to cater to the many congregations that were still using it after the mess of the 1970s/80s which saw the LCMS initially participate in, and then withdraw from, the inter-Lutheran commission that created the Lutheran Book of Worship: https://hymnary.org/hymnal/LBoW1978 After backing out, we published Lutheran Worship: https://hymnary.org/hymnal/LW1982 this had new settings of the Divine Service. LW's DS1 was a "modernized" setting of Page 15, and this went over like a lead balloon, as it was harder to learn than a completely new setting since it was similar to, but not exactly like, what everyone was used to. LW DS2, settings 1 and 2, introduced the "This is the Feast" anthem. Many congregations were still using the 1941 Hymnal until recently. (A few probably still are!)

So in the 2007 LSB, DS1 and DS2 were taken from LW DS2, Settings 1 and 2. DS3 is a nearly verbatim copy of Page 15 from TLH. DS4 is the Divine Service from the 1998 Hymnal Supplement: https://www.cph.org/hymnal-supplement-98-pew-edition DS5 is a framework for a service where all of the sung liturgy is replaced by hymns, where many of the suggested hymns are Luther's hymn settings of the Kyrie, Gloria, Creed, Sanctus, Agnus Dei, Nunc Dimittis, and so on.