California Code, Streets and Highways Code - SHC § 9504

It is the intention of this division that the outstanding bonds and the original assessments shall remain in full force and effect and secured by the original assessments until superseded and supplanted by reassessments and refunding bonds validly and legally issued pursuant to this division, at which time the reassessments shall become the security for the refunding bonds and the refunding escrow shall become the security for any outstanding bonds not exchanged for refunding bonds.