"In your book they were all written" (139:16). What does the verse say was written?

The WEB reads, "Your eyes saw my body. In your book they were all written, the days that were ordained for me, when as yet there were none of them" (139:16). Ordained is the verb yatsar, which Strong's gives as "to mould into a form; especially as a potter". It is the verb of "The LORD God formed man from the dust of the ground" (Genesis 2:7), and for the form used here Brown-Driver-Briggs gives "days (that) were pre-ordained (in divine purpose)". At the verse's last words the Hebrew text has two readings, and the Westminster Leningrad Codex gives both: the word as it is written, and a reading it marks beside it. The written word is and followed by the letters of lo', which Brown-Driver-Briggs gives as "not": word for word, and not one among them. The marked reading differs by one letter (the written word ends in aleph, the marked reading in vav): and with the small word to him, word for word and to him one among them. The WEB's "when as yet there were none of them" goes with the written word. Psalm 100:3 has the same pair of readings, and the chapter on Psalm 100 looks at it. The psalm says no more about the book than this verse, and these notes don't either.