I don't know how to explain it, but I think the HTM is just a part of the shoe name. It doesn't necessarily mean HTM in the sense that we've become accustomed to (premium materials, specially curated colorways). For the first 2 drops, yes, but for these next 2, no.
They aren't called the "Mercurial Superflys", they're called the "HTM Mercurial Superflys". Whereas if a shoe like a "Flyknit Racer" gets the HTM treatment with premium materials/special colorway, it has the HTM added on to the shoe's name.
So the volt and black colorways of these were the HTM "HTM Mercurial Superflys", and the obsidian and grey colorways are just the "HTM Mercurial Superflys".
Don't know if that makes sense, but that's how I see it.