Well, no, they don’t have to be named to be pardoned. It’s called amnesty when applied to a group, and there are several examples in American history.
I know POTUS has the pardon power... does he have an amnesty power too?
To pardon, would/should mean to name each individual.
Then Trump works from that list of names.
Noted - the article specifically mentioned "pardoned". We'll have to see if Obama goes the amnesty route and ends up giving amnesty to a host of felons to boot....