Czar Nicholas, his wife, son and 4 daughters were executed in July, 1918.
The DS timeline here is 1897, so Magda must be talking about some other poor folk who were executed. Unless the Romanovs were who the incantation was referring to and the writers on DS didn't stop and think of the time contradiction.
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Always, Minja
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According to one on line source, 4 of their servants were executed with them.