I looked at the receipt in my account from the flight itinerary page and it shows the upgraded class code instead of the original P... so that means it was reticketed. If they just grabbed the space for the cert, then your receipt would still show the original class but you'd be able to pick a seat up front.

Regarding the Z inventory I mentioned, it started showing shortly after they processed my upgrade so perhaps they saw it opening and it just wasn't refreshed on EF's data yet.