Help with Genealogy Genie achievement (spoilers)

[epsilon828]

I feel like I have to be missing something obvious here, given the relatively high percentage of users who have this achievement, but I can't figure it out. I'm pretty sure I've completed the entire family tree correctly, but I still don't have this achievement.

The only thing I can think of is maybe I missed one of the very final "is this person a Roottree" questions, but Sam told me I got everything "absolutely correct" so that would seem to belie that possibility.

Any help would be greatly appreciated! Thanks!

ETA: Never mind, I figured it out. Somehow I missed the optional photos for the redheaded kids; finally found that ad campaign evidence and got them. (I would quibble that the description is a little misleading, in that by definition the family tree can be correctly completed without optional additional photos.) So for anyone else who might get stuck on this achievement, it's better to think of it as correctly finding all optional photos (there appear to be no superfluous photos; every single photo that you can get can be used somewhere for exactly one person.)