Nothing in your links above indicate that the spyware operates while the phones are powered off (although I relied on a crappy translation of the French). Could spyware mock the shutdown process so that it looks like the phone is powered off while the phone is actually running? Sure it can, but the victim will be tipped off when the phone’s battery is being drained even while it is “shut off”. (And someone who is paranoid enough to shut down their phone would pay attention to that.) . It seems like it’s not worth the effort.