Good question.
I've seen 3, 5, 7, 9 10. I've seen 9 and maybe 10 on largest 2nd generation Dorics. Maybe a 10 on the (larger than 2nd gen) largest late examples of 1st generation Doric.
7's on medium high line 2nd gen dorics.
Based on casual (and occasional) observation, i've seen #5 and #3 on the two sizes of 2nd generation non-seal Dorics, which also -as you probably know

- seem to get non-adjustable nibs, perhaps late in the game.
I have not made a study- though you prompt me to consider doing so- just which nibs go with which pens on the late models. Suspect Syd can flesh this out a bit.
Here are a few pics of the only OS Doric in my own collection- a first gen model in Morocco- really sweet.




regards
david i
http://www.vacumania.com