SFD, catharina is not exactly wrong. Neither are you when it comes to that.
Your 1945 missal takes one position, catherina’s missal or source takes another. I myself have a missal which is judiciously silent on it, but indicates it along the lines of catherina’s idea.
When the Leonine Prayers came out, there was a question of how to recite them. Only in one case was it evident- that of the collect (and even there, there were questions of posture, etc.)
Broadly speaking there were two “main” ways (and you could find intermediates between these as well). The question revolved around what was meant by “cum populo” in the instructions.
- The people (or at least, the server) responded with the “Sancta Maria”, said the “Salve Regina” (and the St. Michael’s prayer when it appeared) together with the priest, and responded Amen to the oration.
A variation on this interpreted “cum populo” more strictly and the people said the entire “Ave Maria” together with the priest
The reason behind this interpretation was that the Leonine prayers of 1884 and 1886 were formerly prescribed in the Papal States and that was how they were recited.
- The priest said all the prayers and the congregation/server replied only “Amen”
Practice (1) was what was observed in many places, most especially Rome, which which regarded s the determiner of such practices. Consequently, some lay missals (like yours) give the requisite instruction.
Other missals, not seeking to decide the question, judiously printed a sole red “R” before the “Amen” at the end of each prayer, indicating that the people should make the response “Amen”.
For the Sacred Heart invocation, the decree indicated that the priest should say it; however, when the Congregation of Rites was asked if the people might respond “miserere nobis”, they replied affirmatively.