False, where does the carbon come from? Fe + N2 + O2 is all there is inside the tank. The trace amounts of carbon in the steel won't amount to anything. We are talking trace amounts of carbon, the steel tank will rust and blow out long before the amount of carbon means anything. You can't make CO2 without having a source of C.
Find a local rebreather diver and look at there bail outs. Especially there deep bail out. The inspection sticker is often expired by several years and not surprising if the hydro is expired as well. The gas is still tested and is fine. But since it isn't used in a dive as long as everything goes right it can be years between refills.