I know this thread is a bit dead and buried, but just to confirm, I've done some experimenting and I think I've worked out what's happening here. When apple says "the last 1000 photos" and "from the last 30 days", we assume photos will be deleted once you hit either of those limits, i.e. whichever we hit first will apply. That's not strictly true, it's whichever you hit LAST. To be clear, you can keep your last 1000 photos in your photostream indefinitely, and as well as that (I have confirmed), you can keep OVER 1000 photos in your photostream if they are taken in the last 30 days. This is when the "30 days" limit applies, which I doubt anyone has noticed as I doubt many people take more than 1000 photos on their iPhone in a 30-day period.