Attribute max and rune upgrades

My Necro is lvl 20 and ascended. My Deat Magic skill is 12 now.
My scar tatoo gives me +1DM and i put a rune on it for another +1DM.

Ok now i got 14 points.
I added another minor DM rune to my tunic but it wont change to 15 (with 3 modified).

Why dosen't it work?

I think you can only use 1 of each rune?

Like you can't put a +3 rune in each piece of your armor for +15...

I would guess because you already have a rune for Death Magic already placed. You cannot place two identical runes on 2 different pieces of armor to receive +2.

I think that applys to minor major and superior. Only 1 if it's death magic not 1 of each.

The runes can not be stacked... You are only able to use one rune of each any type, it doesn't matter if it is minor, major, or superior.

Ah i see. Oh well, there goes my plan for lvl 20 horrors and fiends ^^
Thank you