If Book I on the Calendar is about the Yearly Life of the Church, Book III the Missal is about the weekly worship of the Church, and Book II Common Prayer is about the Daily Worship of the Church, then the Book IV, The Manual is about the Life of a Christian. We are grafted into the church at baptism, we are instructed as catechumens, comforted when we sin in reconciliation, joined to our spouse in matrimony, the women are blessed after childbirth, the minister visits us when we are sick, and the priest burries us when we depart this life.
The baptism material is mostly from the 1549 BCP, except for the part about those of riper years which is from the 1789 BCP. The Blessing of the water, one of three versions in this book, is from the 1549 BCP.
The Offices of instruction are from the 1928 BCP.
The Reconciliation of a Penitent is from the 1979 BCP.
The Order for the Solemnization of Matrimony is from the 1928 BCP
The Thanksgiving after Childbirth, and Order of the Visitation and Communion of the Sick are from the 1549 BCP
The Order for the Burial of the Dead is a mash up of the 1928 and 1549 BCP. The Order of the Burial of a Child, from the 1928 book.
The Memorial Masses for the dead comes from the Sarum Missal.
The admission of lay ministers comes from the 1949 Book of Offices.
Why you might ask this hodgepodge. Well a variety of reasons, but mostly, right teaching, emotional power and beauty. Those for the services that mark important stages in our lives seemed apropreate.