That is interpretation. I understand it literaly. I take the meaning of not written (past tense). I do not take it to mean not to have ever been written.
Again I am of the persuasion names are blotted out, Psalms 69:28, or never to be blotted out, Revelation 3:5.
Those whose names were not written are the subject of Revelation 13:8. But by inference, others whose names were written in the Lamb's book of life since the foundation of the world did not suffer the same fate.
Christ promised to never blot out names written in the Lamb's book of life.