I don't think those AHs trades can occur in the actual AHs since the supply on the bid and ask does not permit it once the market closes.
I think some or all of them are late prints, which can occur for a variety of reasons. With large trades, institutions don't want to telegraph what they are doing.
I have a friend that works an order desk. He gets a commission for filling large orders quietly so that the market is not disrupted while the order is being filled.
As I understand it, it goes like this. Suppose you are an institution and want to buy $1 M shares as cheaply as possible, without your order driving the PPS up as it fills.
You can't put in an order for 1 M at market for the MMs to fill or it will force the price up and your execution will be bad.
But you can place the order with an individual that works an order desk, and he will call other order desks or potential order supplies, and work out matching order fills. He will offer an agreed premium, but depending on how fast the buyer wants to fill, they can take time to keep the price down.
The buyer doesn't necessarily reveal the full size of the order, he just looks for some volume that is available and puts one or more orders together for his customer.
I understand these are phone calls and they complete the parts verbally and send each other required confirmations.
Those fills are not printed onto time and tape in real time. But, once the full order is completed, the order desk will report it, often at the end of trading. At that point, it "shows" up as an AH print, but it is coded to show it is a out of sequence fill.
So, someone probably was buying for indexes or whatnot, but perhaps not at the last minute, as it may seem if you look at the tape and don't see how the orders are coded.
So, the sudden drop in the PPS during the close might be order desk volume but I am not sure how to explain the dropping PPS that is shown, so this could be incorrect for some or all of todays last minute orders.
News 
Market Data 
Discover 
