I think some clarification on what the Individual ready reserve is might be needed here.
When you join the military, every enlistment is actually 8 years long. But the amount of time on active duty can vary. If you spend 4 years on active duty, the remaining 4 years will be IRR. The vast majority of those in the IRR don't attend drills, don't get payed, and don't get any benefits of any kind. They are simply a name on a list somewhere.
It is possible to volunteer to remain in the IRR once your mandatory time is up or too volunteer to return to active duty while in the IRR, but when you do not volunteer but are called back to active service (up to 4 years after leaving originally), its considered an involuntary callup.
So basically, up to 4 years after leaving the military you can be told to drop what your doing and report for duty. You can say its their own fault for joining the military in the first place, but at the same time, the IRR is one of those minute details the recruiters don't tend to spend much time on.