In my experience and from what I gather with OSK, if it is still on the site available for purchase/order, even if it is past the original cut off date, then they still have stock allocation available. The 'cut off' date is when OSK have to get their own initial allocation order in by, but the item itself won't close from being orderable (unless the manufacturer wants it pulled after a certain date) until that entire allocation that OSK orders has sold through. So if OSK has pre-sold 200 of item-x before the cut off date, they might order 220, and item-x will remain on site until those final 20 from their allocation order (pre)sells through.
Long story short, if it is still there to buy you can still buy it. I've ordered a lot from OSK and have never had an availability issue on anything I was able to ourchase and pay for.