I found the language I was looking for…
Rule 5 Players, Substitutes, Equipment, General Rules
Section 3 Changes in Position
REPORTING CHANGE OF POSITION
Article 1 An offensive player wearing the number of an ineligible pass receiver (50-79 and 90-99) is permitted to line up in the position of an eligible pass receiver (1-49 and 80-89), and an offensive player wearing the number of an eligible pass receiver is permitted to line up in the position of an ineligible pass receiver, provided that he immediately reports the change in his eligibility status to the Referee, who will inform the defensive team.
He must participate in such eligible or ineligible position as long as he is continuously in the game, but prior to each play he must again report his status to the Referee, who will inform the defensive team. The game clock shall not be stopped, and the ball shall not be put in play until the Referee takes his normal position.
This is not just about the one play, which is perfectly legal on a stand-alone basis. It's about the entire series of plays.
IF Manatee and/or Vereen changed their eligibility during the series without substituting that is a violation. I thought that is what happened, and what the announcers were flagging for our attention. I don't know if they above description is the official rulebook, or college or pro or whatever, but I thought that a player who was out there could not just change his eligibility on the fly if he was already in the game, which it seemed that Vereen did.
Was Vereen on the field the whole time, or did he sub on for that play? If he subbed, he would have had to report immediately and the Ravens would have had time to adjust due to the substitution. It looked as though Vereen reported to the official on the way over to his position on a no-huddle situation, which would not be immediate and would also be a change in his eligibility which is illegal (assuming I've got the right rules up there).
IF the Patriots declared properly and the Ravens were given time to understand the changes from the beginning of the series or the player's continuous participation in the game, then the Ravens just got outsmarted which is perfectly legal.
IF, as I thought happened, Vereen was in the game on the series, played as an eligible on one play, and then switched (or even, on a single play, reported late which looked like happened on the completion to Manatee) then the plays should be disallowed.
The rules are pretty clear that you're not supposed to be allowed to accomplish this type of confusion against an "aware" opponent.
So it's not just about whether that play was a legal alignment, it's whether the substitutions and reporting were done properly and in a manner that allowed the Defense to adjust. Yes, that involves time as an element.
Was Vereen ineligible the whole series (or the whole time he was in there continuously?)?
If this is the wrong rulebook, then I'm a doofus but this was my immediate thought process about it.
I'll continue to differentiate this from the standard unbalanced formations…but at the same time if Vereen subbed in and declared ineligible in a timely manner on all three plays then I'm wrong.