Later, after the university denied him access to the codex, Mordechai Breuer began his own reconstruction of the Masoretic text on the basis of other well-known ancient manuscripts. His results matched the Aleppo Codex almost exactly. Thus today, Breuer's version is used authoritatively for the reconstruction of the missing portions of the Aleppo Codex. The Jerusalem Crown (כתר ירושלים, Keter Yerushalayim, lit. "Jerusalem Crown"), printed in Jerusalem in 2000, is a modern version of the Tanakh based on the Aleppo Codex and the work of Breuer: It uses a newly designed typeface based on the calligraphy of the Codex and is based on its page layout.
Okay, question answered: the missing parts were reconstructed by Breuer.