Originally Posted by Redonkulous BP
It's hard to describe. I'll put it this way, if you save 10 concrete shots by not using them on Wily 4, you can't use that same amount or even less somewhere else - it will void the achievement. This happened to me on Wily stage 2 where I died and had to re-use the laser trident to destroy a block underwater. It voided my achievement and I had to play again.
However, on the same part you are talking about with the phantom blocks, I screwed up a rush coil, and re-used it. I made it the second time, and I got the achievement on that play through. So, it may just be that you can't die and re-use something. The laser trident voided the achievement, the rush coil did not. this may also mean that Rush energy does not count as weapon energy, but I am not sure.
Rush energy does count as weapon energy. I had the same issue durying my runthrough for Conservationist. I used 2x Concrete Shot in the room where you first encounter the projectors much like how you used RC 2x. My achievement still unlocked.
It could be that the room allows for one mistake. I don't know. it'd be pretty hard to confirm it.