With all due respect, this is a slightly different situation.
Your lawyer is correct in saying that the new priority date will be in the approval notice. In case it does not come, the lawyer can make explicit Service Request to request porting.
I am in a situation where all this has happened and USCIS responded by saying that my date could not be ported.
Originally Posted by rorlig
We (my wife's i140) is in a similar situation. They gave her a new priority date on the receipt notice. The lawyer said that the priority date is ported successfully would be on the new I140 accepted notice and not necessarily on the receipt notice. Is this true?