Mastery / Prudence main quest

[HFoC]

"Invest at least 6 (resp 11) Codices in one of your Explorers (resp. Geologists)."

Does that mean they have to be invested in one and the same specialist? So eg. 3 codices on one explorer and 3 on another doesn't work?

[Kit_]

has to be on just the one

[Xibor]

has to be on just the one

[correction]

In my original post I was mistaken concerning geologists - Kit_ is correct. I took another look at my geologists and the fact that I have 8/11 on that quest, and they are all on one guy.

They do need to go on one specialist.

[Kit_]

I disagree. It reflects the total of the books used regardless of if they are spread out or not. I'm pretty sure you couldn't get 6 codex on one explorer because of the total book limit and the number of books you need to use to get to the point of using codex.

I'm part way through that one and my codex are spread out.

wrong, the quest does ask for them to be all on one. I have completed that quest myself. and had others who have had more than 6 spread over several specialists, without it counting.
Also it is perfectly possible to get all of them on the one explorer; 21 books total, if following the way BB intends you are supposed to put 5 books on each line and 1 at the very top, so 5 manuscripts, 2 lines with 5 tomes each, 1 line with 5 codex and 1 codex in the top. The issue many people come up against is that they put too many books further down. You can fiddle how many books you put lower down ie extra manuscripts and less tomes, but have to keep an eye on the numbers used.