Recently, administrators said that because the server problem, if you submit a scan but don't receive any rejection or see it in the gallery, you should try again. From previous weekend to yesterday, I've tried submitting 4 scan s, and when I didn't see it in the gallery or receive rejection after 30 mins, I also tried uploading again. But only 2 of them were accepted. At first, I thought that the other 2 scans may be in process. But in the next day, I saw there were the same 2 scans in the gallery which were upload by other users, and I get rejection (says I upload the same pics, blah blah blah) instead. I am sure when I submit them, they did not appear in the gallery. Why do you adms accept the latter but reject me the former. Thanks.

About the two scans that were rejected: I am guessing that the uploader uploaded the two scans before you did, but it was still in queue, therefore, it doesn't show up in the gallery. So, when a mod cleared the queue, he/she approved the two scans first because it was submitted first and when yours came along, they were considered as duplicates and thus, were rejected.

Oh, then how do I realize that there is the same scan in the front of mines in the queue? Or I only can just try as fast as possible to upload them before others? Thanks.

P.S.
http://www.animepaper.net/gallery/scans/The-Melancholy-Of-Haruhi-Suzumiya/item75823/
http://www.animepaper.net/gallery/scans/The-Melancholy-Of-Haruhi-Suzumiya/item116840/
I thought these two scans have the same content. The difference between them is one of them contains calender, the other do not. Can this situation be explained that those are two different scans? Thanks again.

Basically you have no way of knowing if a scan in the queue is a duplicate of your own. What you need to check however is the gallery. If staff find that you've submitted something unaware that the same image is in the queue it will likely lead to rejection but without the accompanying fine.

Ideally if you're submitting scans you've made yourself as is preferred all of the above is entirely moot.

That would be a duplicate and needs to be reported. The usable content is the same and the moderator who approved the second image must have missed the first.