They are numbered 0001, 0002 etc. That's how they work, they just have two random digits at the end.
Look at your clips, they're all sequentially increasing in number (in the first four digits of the name) and then have two random digits attached, so it's something like:
0001aR.mxf
0002Q3.mxf
00031Z.mxf
The confusion really sets in when one of the random digits is a number; that makes it look a lot more random than it is. Just look at the first four digits, not the last two.