the unfortunate tendency of some sellers of vintage pens to call nibs that have lost their tipping and been re-polished "stubs" leaves a bad taste in my mouth, so I try not to perpetuate half-truths like that.
You could easily also have a Fine round-tipped nib on which the iridium tipping has largely worn off (or been polished off) through repeated abrasion against writing paper, micromesh, emery boards, sandpaper and what not, but still puts down lines of (say) about 0.4mm wide consistently. That's just a Fine nib — that arguably is in poor condition and of questionable longevity, no? If you say "it isn't really" a Fine nib and the statement is a distasteful half-truth, then how would you categorise its nib width grade and/or type?
The volume and condition of the tipping on the nib is logically separate from the geometry of the contact area between nib and paper, and I think we're agreed that "Stub" as a descriptor of nibs refers only to geometry. There are wider or narrower Stub nibs, thicker or thinner Stub nibs, Stub nibs with metallic (tipping and body) material in good condition or poor condition, "factory" Stub nibs or Stub nibs that started life as something else. Are any of those more "real" as Stub nibs than the others?
In my opinion, there is nothing sacred about Stub nibs as a classification that demands a higher level of discernment. It makes me think of electrical and mechanical engineers declaring that "software engineers" have no claim to being engineers because the latter do not meet the Institute of Engineers' membership requirement of having completed a four-year Bachelor's degree in Engineering; at least in that case there is turf, standing and prestige at stake in the competition for higher pay, etc. Stub nibs don't speak for themselves or actively want to make their own classification a more exclusive one.
I will however argue that the term "stub" refers to a more relaxed geometry than "italic" and that the closer to a crisp edged geometry and the wider the differential between cross and downstroke the less a nib falls into the category of a stub.
Relative to each other on a continuous spectrum, yes. On the other hand, even if it lays down 1.1mm wide downstrokes and 0.3mm wide cross-strokes, a nib with a straight edge of 1.1mm flanked by rounded corners of 0.4mm radius isn't going to be an "italic" nib in anyone's book, is it?
Please note I'm not trying to argue against any personal preferences in writing outcomes, but simply what does or does not (or could or could not) fall within a classification or category as a shared understanding when communicating with vast numbers of other users, especially when they presumably have different levels of experience and different personal preferences. There ought to be nothing subjective when there is an allusion to fact (cf. "half-truths").
Let's give each other due respect, and approach discussion rigorously. I believe we're all peers and equals here as fellow hobbyists, with common interests in the acquisition and use of fountain pens, but no shared values and no obligation to offer each other moral support for one's narrative.
Don't think 'cos I understand, I care
Don't think 'cos I'm talking, we're friends
— '6 Underground' by Sneaker Pimps