Here's what you do.
You call for a target and it comes out in one piece, alone, on time, is not an odd color, but is illegal because it is ten degrees outside on what's being thrown or is a flipper.
You don't shoot at it, (If you do, as WPT says, it's scored in the usual way) and, as you take the gun down, you tell the scorer that you didn’t shoot because it was illegally right or left or it was a flipper.
If the scorer agrees (which he or she will certainly do, the first time anyway . . .) he or she should say "No target" and you just go on shooting. If the scorer disagrees, the target it "lost." It is _not_ a failure to fire, since you voluntarily did not fire. You had a good and fair reason not to, but you declined to shoot voluntarily.
If the scorer has no idea what you are even talking about (it sometimes happens) , unload your gun, walk back to the chair, and explain the rules and that you think that the target fell under the "illegal target" rule and he or she should rule "No target."
I've never encountered any problem doing this and I don't think you will either.
If someone on your squad is just failing to shoot targets, ask him or her what is going on. Thereafter, ask about any repeats. They usually go away.