The Canon shutter counts roll over every time they hit 9,999.
On a camera that old, it is likely that the shutter count has rolled over several times, especially if there is an _ within the image number!
I've only had my Rebel T5 for just under 2 years, and I've rolled the shutter count over at least twice in that time!
The shutter count does not roll over! The file number rolls over.