I've moved on to a deep dive into the Dark Age, and noticed that pretty much none of the units in the TR3150 "New Tech, New Upgrades" section have a MUL entry.
Maybe they don't have record sheets (I also noticed they weren't on MegaMek or SSW), but that hasn't precluded other MUL entries that don't have record sheets. Plus, I noticed that at least one is referenced in the new Rec Guides (Hatchetman-7D in RG12).
Is this errata, or are they on some long-dormant to-do list?