I didn't realise January's quest was the first time the Descender appears in Series 6. Perhaps that's why it's one of the few specific Knightmare scenes that I always remembered from childhood.
The Big Issue has certainly had me scratching my head this evening - I've gone back and forth on it several times while considering the evidence!
I agree we're left with a strong impression that there's only one Dreadnort (I've always tended to think of him as a unique creation) and there doesn't seem much point in having multiple Dreadnorts around.
I like to incorporate as much on-screen content as possible into my headcanons, so if Pickle had actually said "It's one of Lord Fear's Dreadnorts" in that scene, I would've accepted that he knows there are others. But the way he words it like an afterthought ("That's Lord Fear's Dreadnort - well, one of them") might suggest Pickle himself isn't sure if there's one or several.
It's not the only such quote in the series, though... Pickle again says "that's a Dreadnort" in the next episode, and Elita says "If you should meet a Dreadnort..." while speaking to Sophia, so she must think there's more than one. More significantly, Skarkill in the first episode asks Lord Fear for "the loan of one of them mech... well, that ruddy great metal warrior thing", which seems to imply there will be several if there aren't already. Lord Fear replies with a comment about "the Dreadnort", but he could be talking about it as a general concept rather than implying there's only one, or perhaps he's only built that one so far, as Martin suggested. Lord Fear does tend to produce a few of his monsters (Frightknights, Skeletrons etc), and Tim Child refers to "Frightknights and Dreadnoughts", plural, in The Quest.
I do think either interpretation is valid (there's always room for "character error" as they call it on the IMDb), but overall I have to conclude there are multiple Dreadnorts, even if I find it difficult to visualise!
Incidentally I think Dreadnort's lines are definitely live in the next episode as he ad-libs "Out of my path!" when the advisors tell Ben to start walking at the same time, which could've really messed up the visual effect if Ben had stepped in front of him. (Pickle has to hastily intervene as well, telling him to stay where he is!) And perhaps because of that, he adds "Pass and live in fear" rather belatedly just as he's walking off-screen.
I would love to know what Jamie's team did to deserve their fate, too! (I even wrote them a filk once.)
I can't agree that the Stormgeists look unsettling - I commented during my first watch-through that they look like something out of Button Moon, and I've never been able to shake that impression! (I think they vaguely remind me of the plastic bottle characters, combined with the slightly rubbish puppeteering when things are supposed to be flying.) So they just don't work for me as a threat, apart from that one time when Sophia was trapped in the Descender with a huge one.
Wow, I've never noticed any real-life issues with Rayner Bourton's leg in this series - what an interesting observation! I'll have to look out for that when I'm watching in future. (Shades of Mark Knight's broken arm in Series 8.)