You're talking about something like Mir? The reason they couldn't predict its re-entry is that it was going to very lightly skim the upper atmosphere and therefore feel just a tiny amount of drag over many orbits. The upper atmosphere is not unlike the surface of the ocean. There are places were the atmosphere was a little thicker and would just touch Mir, slowing it a little, and other places were the atmosphere wasn't as thick and had no effect.

There's no way to predict when all of that will build up to cause a reentry.

On the other hand, what we're talking about here is intentionally deorbiting these rods. That's very easy to control and should be really accurate.