It's been kind of a weird few years for Universal Century scholarship, with very little fresh source material being produced, and a somewhat uneasy integration of the Origin back story into the animated continuity. And the recently launched Mobile Suit Discovery series, whose mandate is to fill in gaps in the mobile suit development history, has so far just made it even more complicated.
That said, I'm very much looking forward to the release of the YMS-08B Dom Test Type so that I can look up its skirts!
Let me back up a little. Recently, I was working on profile text translations for an upcoming Gundam game, and I noticed a throwaway reference to the Rick Dom having added thrusters in its skirt and legs. Recent model kits have depicted both the standard Dom and the Rick Dom as having these supplemental thrusters, but it turns out that a lot of game profiles (and the Japanese Wikipedia page) characterize them as a new feature added to the Rick Dom. And indeed, these first appeared in the new footage for the Gundam III movie as a unique feature of the Rick Dom and Gelgoog.
I've devoted a few previous threads to speculating about the possible output of these kinds of secondary thrusters, but right now I want to step back a bit and consider the question of their actual existence.
It's pretty clear, for example, that these thrusters aren't present in the standard Gouf or in the MS-07C-5 Gouf Test Type which was used to gather test data for the Dom. The MS-07C-5 does have a ring of vents around its legs, which resemble those on the YMS-09 Prototype Dom, but there certainly isn't room for anything similar in its skirt armor.
Interestingly, the Prototype Dom doesn't seem to have them either. Aside from the aforementioned vents, it has a single big thruster on the back of each leg, and its relatively streamlined skirt armor doesn't seem to have room for any thrusters. Katoki's Prototype Dom design for the Zeonography series has a bigger skirt with thrusters in it, and this feature is carried through to the Dom Cannon variant, but this is a distinct change from Okawara's original design.
In other words, the MS-07C-5 probably has some kind of leg thruster (inherited from the Gouf) and nothing in its skirt; the Rick Dom definitely has leg and skirt thrusters, in addition to those in its feet and backpack. But it's surprisingly hard to say at what point in its development these features were introduced.
Consider, if you will, some other examples. In First Gundam, we can clearly see thruster exhaust coming from the skirts and legs (and backpack and feet) of the Black Tri-Stars' Doms. Since these were delivered from space, rather than the California Base, it's possible that they're actually newer models that incorporate Rick Dom features.
The Dowadge from ZZ, of course, has the leg and skirt thrusters - it's one of the few cases where they're even listed in its specs.
The Dom Tropen, on the other hand, never had clearly depicted skirt thrusters until Gundam Unicorn. And due to the hovercraft "clogs" on its feet, even if it has thrusters in its legs, it couldn't use them.
The Pezun Dowadge, as designed, doesn't seem to have room for skirt or leg thrusters. But Katoki added them in his Zeonography design anyway.

This is all complicated by the fact that Doms and Gelgoogs hardly ever use these supplemental thrusters. Char's Gelgoog, which has no backpack, obviously relies on its skirt thrusters for propulsion. But I don't think we've ever seen a Gelgoog using its leg thrusters in the animation, and versions with backpacks tend to use those thrusters instead (or, in some versions, the extra thrusters added to the tip of the skirt). For the most part, the skirt and leg thrusters are only used as the mobile suit rushes into combat, pushing it straight upward; they don't seem to be used for combat maneuvering. So we can probably think of them as boosters with a limited fuel supply, a bonus feature added as an afterthought to take advantage of the extra space within the mobile suit's flared armor.
So where does the YMS-08B fit into this pattern? We'll have to wait and see!
-- Mark