Why not break the rifle down and do a quick check before buying it? As it literally takes just a few seconds. This way you are 100% sure either way. Personaly If I buy a new one Id ask to look at the rilfe BEFORE any paperwork is done, check the blue springs AND see if its one of the newest serials DUU.

If not you may as well get the rifle you are going to be satisfied with. If that means looking at a few to get the newest serial number you can, whats the hurt in doing so. YOU are the customer, and should be allowed to buy THE gun you want. Not just any serial they happen to "get rid of". But any thing close to that DUU serial range will be fine.

Im NOT saying the others are bad, Im just informing you of the newest serials/models out as of now. I wasnt aware of the serials when I bought mine, and got lucky to get a DUU3XXX model rifle. Made in last days of June this year. congrats on the future purchase!