Excluding the rest of the sentance, yes. but the latter part of the sentence indicates the part to be attached to or part of the firearm. Earmuffs reduce the report reaching your ears but the report is still there outside of the firearm prior to the pressure wave reaching the earmuffs and is still present to passerby. The controlled silencer forces the sound through itself (thereby diminishing it) before releasing it to the environment. range baffles, a stack of tires, and ear-pro do not attach to the firearm and act upon the sound after it has been released to the environment in-full.
I am just debating this for kicks, so please take it as such.
Report might be defined within the law elsewhere ( I have not looked), but by common definition is a sudden loud noise or of like an explosion or gunfire. The NFA paragraph does not speak to when the the reduction must occur. I am not disagreeing with the interpretation, I just found it interesting that it is not more defined within the NFA.
I also do not see where it specifies that it must be attached to, or part of the firearm. It does state that it includes any combination of parts that are intended for use as a firearm silencer or muffler (broadly defined earlier), and that it is intended only for use in such assembly or fabrication. I certainly get that it is implied that the assembly or fabrication applies to that of a portable firearm, but it does not exactly state it that way.
It just makes me think about the is it a brace or is it a stock debate that has gone back and forth (interpreted different ways as different times). I've also read about the oil filter thread adapters, and based on the language in NFA how the heck are people getting a tax stamp for just a thread adapter without the reduction of report?
Anyway... I'm really only half hearted arguing this, just that it was interesting.