It definitely could be brass, good analysis. It's unique in the sense you dont really see slip cap ringtops, and especially at this size, and as a lever filler. The 14k Warranted nib is definitely the best feature, with a nice flex to it, but very small and hard to handle.
At risk of playing Grammar Cop, I do think it's good to keep straight general and hobby jargon
"Unique" is an oft-abused word, often used for "uncommon" or "rare" or (heaven forbid) either "interesting" or "valuable".
Doesn't mean that. Means only one known when used as a modifier for a noun, though there is room for context specific usage, such as "unique in my experience", which of course means little or much depending on the power of one's experience or "unique to Canadian production" if something made in many places had a feature found only with Canadian items. That something is quirky and even interesting ought not to invoke uniqueness.
Too, while I can keep open mind as to what anyone finds interesting (folks collect cars, art, pens, PEZ, hell they can collect petrified orange peels if they want), there also is something to be said for avoiding over inflating the significance of weak items, based on playing up quirks. Exceptions exist, and I can explore some exceptions I recognize (noting others may disagree).
But, this pen is a trashed condition low-name (lo-nami, as some say) poorly finished critter. Baby pens (extra small) have charm. Finding nice writers in even dealer junk boxes for a buck can be fun. Learning how to fix one's own pens as part of hobby growth has great merit. Exploring the history and context provoked by consideration of any pen... all good. But, I do get sense of... inflation... in discussing this one. I have trays of pens from collection purchases that I'd sell for $1 to $10 the pen. This one would seem to fit in with those. There are probably hundreds of lo-name, lo-quality pen labels from that era.
Rant done.
-d