EVE Technology Lab

I'm wondering if someone can help me with a little problem:

I've been working on something to calculate a bill of materials. This works for the most part. However, I've found some T2 items with unsual numbers.

e.g. The Miner II material requirements includes 532 tritantium. As with most T2, the manufacturing requirements include the T1 variant, the Miner I with the recycle flag set. So I look up the Miner I requirements, which turn out to include 1192 tritanium.
532 - 1192 is -660 but I assume that trit does not come spewing out every time you manufacture a Miner II.

I assume that this simply means that zero trit is required when manufacturing the Miner II. Does anyone know if this is generally correct?
So if the result, after taking away the recycled item's material is < 0, can I simply assume it to require 0 and that's it?

Thanks