Your comment reminded me of a funny thing. I did a couple years in the Alaskan prison system. The prison I was in served two tacos every Wednesday for lunch.

I worked in the computer lab, and as a lark, I wrote a cute program where an inmate could input their projected release date, and the program would tell them how many tacos they had left before their release.

Years later, after my release, I learned that the department of corrections had been sued by an inmate who alleged their "Taco Time Calculator" had miscalculated his sentence.

Any or all of the above. If you find yourself making the statement "we couldn't fix your bug because the developer was on leave for six months" then there is something mind-bendingly wrong with your world. Six months is enough time to hire another developer to fix the bug (even if it's a temp because they're coming back). You don't just... leave it broken for six months.

Well, apparently you do.

Maybe the system is byzantine that only this guy understands it well enough to make the change.