During the Ninth Hour's Daytime Litanies of Great Friday's Holy Pascha, why are the first twelve "Lord have mercy" said without the verses?
I think you are referring to the verses of "O King of Peace" which we stop chanting from the sixth hour of Great Friday. This hymn is chanted to conclude the Prayers of the Hour during the Holy Pascha; and since we pray continuously from the Sixth Hour to the Twelfth Hour on Great Friday, we do not chant it. During these Hours of Great Friday the Church congregation says, "Lord have mercy" twelve times with the long melody. This is preceded with the Daytime Litanies. We say "Lord have mercy" twelve times representative of the 12 tribes of Israel and the 12 disciples. Lord have mercy is to glorify the Lord Jesus who is on the Cross; who has the power, the glory and the majesty forever. The congregation may or may not divide in half to repeat "Lord have mercy" facing the north and south. Also as you may already know, we do not pray the Psalms of the Agpeya during this week as they are replaced with the Doxology of the Pascha. Only the prophecies fulfilled on the correlated day of the Holy Week are read. Up until the Eleventh Hour, these prayers are prayed "outside the camp" (Hebrews 13:13) since the Lord Christ suffered and was crucified outside Jerusalem.