Unchained Summoner - Eidolon DR stacking with Aasimar FCB?

[Divvox2]

1) I am aware DR from different sources don't stack.
2) Aasimar FCB stats that "Add DR 1/evil to the summoner’s eidolon. Each additional time the summoner selects this benefit, the DR/evil increases by +1/2 (maximum DR 10/evil)." (emphasis mine)
3) The Agathion, Angel, Archon, and Azata Eidolong subtypes all provide DR/Evil at some point in their progression.

Is this an exception of DR stacking, or am I missing syntax somewhere that does prevent this? It's a pretty clear rule as far as I have interacted with it in the past, but I am not aware of any examples that use the word "Add" when applying DR to something.

Can anyone provide me with evidence that these two sources don't stack?

[Entryhazard]

It wouldn't have stacked if it had said "gains" or "gets" but "adds" allows for stacking. Maybe it's unintended but those are the actual rules and English language ¯\_(ツ)_/¯

[Divvox2]

Bump, just hoping to cast a wider net than 1.

[Imbicatus]

It says add, so I would allow it, but it also says maximum DR 10/evil. If you get to DR 10/Evil from both sources, then the FCB won't take it past that. And if you got DR 10/Evil from the subtype alone, then all of your FCBs are wasted at that point.

[Mr. Jingles & Eduard Delacroix]

I would rule that the FCB only takes it to a maximum of DR 10/Evil but whatever the subtype allows is the base so basically maxing it out at +10/evil to that DR. So say the base gave 5/evil it would be 15/evil.

[Divvox2]

I expect table variation on the 10/Evil limiter, which is fine (for my purposes), though I'd think the FCB spoke specifically to what it could grant. Related eidolons only get 5/Evil before level 20, so dropping 9 FCBs into it would get it to 10 and grant the improved DR.

Any additional arguments to be made, or is 'Add' pretty clear?