回复：pjiang， 863211：PD可以保留吗？

There is a USCIS memorandum that states that only where the I-140 is revoked for misrepresentation or fraud are you not able to carry the priority date (PD) over (PD transfer).

So, for my understanding, once I140 is approved the PD is yours unless your employer revokes the I140 a for fraud which he cannot do without evidence and the employer himself puts itself at stake by doing so. So, you are completely can transfer your previous PD to your later I-140.