Unlike the Stormtrooper, we still don't have very thorough concrete reference for the Scout costume, other than what we can see in stills. Perhaps some did have neck seals, and others didn't. We've already seen that some greeblies were upside down & some weren't. Some images were flipped, while others weren't. So even some screen reference is questionable.
Also, just because something was thrown together from the archives, doesn't mean it's quite right. For example, even the Star Wars Visual Dictionary has incorrect code cylinders shown for officers, and everything in that book was supossed to be screen-used. I believe we should focus on what was intended for them to be wearing. The Scout who had his uniform stolen by the Rebel Trooper had a balaclava on. That pretty much says to me that that's what they were intended to wear, or else we would have seen the rebel with a neck seal.