This has happened to me a few times. Earlier this year all my Fall PP pix from last year suddenly reappeared in my account. It was 4-5 months after that fact.

Since I had already ordered those on a CD I really didn't want them again. I started to delete them and realized it would take me forever (over 1500-I did a share). I sent DisneyPP an email asking them to remove all pictures taken before a certain date. They did and I continued with my new order.
I would send them an email asking them to remove the older ones if you want. Personally, for me, all the extra photos just made the editing process take a little longer for each photo.
Don't worry about uploading your new ones. They will be fine. Once you enter your new ones you'll see new expiration dates on those. 30 day from your upload date. If you don't want to contact Disney PP about removing the older ones, you could just want until the older ones fall off-Aug. 3rd, but it won't affect your new ones at all, either way.
This seems to be a computer glitch that happens sometimes.
Oh, and the good news was when I contacted Disney and they removed the really old ones all my other photos expiration dates changed to a later date. They gave me 30 days from the date they removed the older ones. Don't know if this always happens but it let me add a few more trips to DLR on my order (we have DLR AP

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HTH. Let me know if you have any more questions.
You're welcome!