Dropbox uploads TOO fast

Hi All,

This may sound like a strange glitch. But, I use dropbox to send important files to paying clients, so I want to try to figure out what is going on to make sure that I don't send people broken links or corrupted files.

Let me explain. I added a 25GB video file to my dropbox folder as I normally would. Files this size typically take 12-24 hours to upload to dropbox. I don't have gig speed internet. However, today, dropbox reported that the file was uploaded within 5 minutes!

Windows explorer and the sync queue all indicate that the file is uploaded. When I open dropbox on my browser and my mobile phone I'm able to watch the video in it's entirety. As one additional check I opened it in a different browser where I'm not logged into dropbox and it even appears to play fine there. Although it only allows me to watch the first hour of content since I'm not logged in there.

I have not tested watching the video on another computer outside my home. 

While I would be thrilled to upload massive files in minutes, I want to be sure that the files aren't getting corrupted or clipped. I don't want to send a link to a paying client only to find out the file never uploaded. I'm particularly concerned because I uploaded the same file yesterday (under a different name) and the client said it came through corrupted, Yesterday it took 14 hours to upload. 

I can think of a couple of possibilities right now: First is that I uploaded an identical file yesterday (with a different name). Is it possible that dropbox somehow recognizes that these are identical files and just uses the first one as a stand in? 
Second, is that dropbox is glitching out but since I'm checking the file from devices on the same wifi network, it's reading them over the local network.

Has anyone else experienced anything like this? If so, any help would be appreciated!

Thanks!