Rereading gtn and Im stuck on Colum's missing finger. What happened to it?
Was it a battle injury? Do the Templars truly live up to their name and see actual battle?
This, to me, seems incredibly risky. To go through all the effort of getting one heir with a matching cav and then risk them both potentially dying in combat, after going through the trouble of making three potential cavs to get a blood type match, is just not worth it. I mean, Judith, heir to the official military house, hadn't ever seen actual combat. And Isaac was going to join, be we know the fourth uses stored genetic material, and is an appendix of the fifth, so his personal survival didn't matter as much. So if it wasn't likely a battle injury, and cavs of the Eighth need to be a blood type match, I have a second theory.
What if Silas ate it? (Or, at least, has it)
I admit, it seems waaay too much like something heretical for the eighth to do, but, they're also soul siphoners. What if the necro having tasted/consumed a small part of the cavs flesh allows them to call them back easier? Maybe this is why a blood type match is so important, because the flesh is more involved than it would appear. We know Ianthe uses a similar practice to boost thanergy, and while the others think it's gross it's not said to be openly heretical. And it's an essential part of the Lyctoral process, a requirement to merge souls. And we know that souls, to return from the place beyond the physical, need a link back. The link to the corpse is the strongest.
So even if Silas didn't eat it, it's not ridiculous to think he wouldn't at least have a preserved Colum finger on him. Or somewhere on the Eighth. To make it easier for Silas to "bid him return"
(This line is so specific too, and the way he mentions how long it took Colum to come back... hmm... the things we don't know)
Im not sold on this theory, personally. Im not putting all of my eggs in this basket. There could be plenty of other explanations. I think it's reasonable that Colum could once have gotten into a scuffle meting out the "Emperors Justice", but would it not be mentioned? The detail of his missing finger keeps jumping out at me. And I likely missed a line about it. But it's like a gap in my teeth.