In example A you cannot tap to add a creature to the opponents side because there isn't a point in the untap step where you can do anything. You go to untap step permanents and such untap then you're immediately in the upkeep step at that point Oath of Druids has already checked and saw that the creature count is 1:1.
Not quite. It has checked the creature counts in that it has had it's target assigned but the ability goes on the stack and thus anyone can respond to it.
@JadePhoenix Heh, funny.
The original wording had the intervening if, and when they cleaned up the wording the functionality stayed intact for a completely different rules intricacy. Interesting.
I only just noticed this seemingly recent change as a result of this thread. Good to know these things but very strange that they would bother with errata that doesn't change the functionality of the card. They must have just wanted to make this kind of intricacy more obvious to players. Not sure it's more obvious though.
@Greg I too have had a fair number of judges give the wrong ruling on this card as well. It can be extremely frustrating when it directly costs the game. It always comes as a surprise to discover how few people understand the details of how the Exodus oathes work especially considering the fame of Oath of Druids; however, I also had to seek out a definitive answer in order to learn the interaction as well at some point so I can't resent an Opponent for just not knowing.