Hi. While the immediate response is that it's always best practice to refrain from providing "final" waivers - whether conditional or unconditional - until after everything on the project is completed, that doesn't help much here.
The good news is that in California the form for waivers is set forth by statute, and compliance with the statutory form is required for the waiver's effectiveness. The form for a conditional final waiver is set forth by § 8136 - and the waiver contains the following provision: "Rights based upon labor or service provided, or equipment or material delivered, pursuant to a written change order that has been fully executed by the parties prior to the date that this document is signed by the claimant, are waived and released by this document, unless listed as an exception below." (emphasis added).
Accordingly, labor or material furnished after the date the waiver was signed may be exempted from coverage by the waiver - despite the fact that it was originally intended to be a "final" waiver. As noted previously, though, the best practice would be to ensure the job is over prior to using a "final" waiver moving forward.