No such inferrence to ignore. It is a popular presumption.
An interpretation of the English translation "are/were not written in the book of life." Revelation 13:8. Revelation 17:8. . . . ου γεγραπται τα ονοματα . . . .
NASB Psalms 69:28, ". . . May they be blotted out of the book of life . . . ."
NASB Exodus 32:33, ". . . will blot him out of My book. . . ."
NASB Revelation 3:5, ". . . He who overcomes will thus be clothed in white garments; and I will not erase his name from the book of life, . . ."
To infer other names were written in the Lamb's book of life is an inference, not a presumption. To presume names were written in the Lamb's book of life before the foundation of the world is a presumption.