History tells us that any additional tickets that become available only go on sale to those who were eligible to purchase when the allocation first sold out.
It should therefore be possible for any in tiers 1, 2 and 3 to purchase any returns.
I registered for this one in case I didn't get Ajax tickets, as I can only afford one trip.
I'm tier 2 anyway, so won't affect the number available Monday morning, but one less person in the scramble, as I was successful in the first minute scramble for Ajax.