i should specify that the text description doesn't reflect their headlessness. in fact they have a healthy beard

i should specify that the text description doesn't reflect their headlessness. in fact they have a healthy beard
It's something to do with how they were generated by the world in advance, but then pulled into your game ahead of their time.
sometimes migrant dwarves can have negative age. their size also reflects the age so the lack of head could be a side effect of the negativeness.
Migrant dwarves occasionally have their birth dates out of sync with your in-game calendar- something to do with how the simulation deals with time outside of fortress mode, I think?- and unfortunately, dwarves are not allowed to have a head until they're at least 0 years old.
Thanks for this; I actually logged in to my 15-year-old Bay 12 Games forum account to poke around the bug reporting subforum to see what they were saying about this, and sadly discovered the whole discussion had moved to Discord.