PCB labelling bare part number vs assembled part number
Number 4 is a common practice and avoids the ambiguity inherent in the other options. Contract manufacturers tend to be familiar with it as well. You can / should put the PCB PN on the PCBA BOM. You didn't mention serialization, but it also plays well with that since you can keep the PCBs traced by lot (typically printed somewhere on the PCB, perhaps near the PCB PN) while tracing the PCBAs individually - just have the adhesive sticker contain a unique PCBA SN as well as the PCBA PN. It's convenient to include a QR or bar code.