When I registered for the ACT, my school encouraged me to put “American Indian” (alongside “White”) as my race to look more diverse and I didn’t really think much of it (I have a great-grandparent who is American Indian, so it isn’t a lie). But, I have never had any DNA testing done and I do not have tribal citizenship. I already sent my ACT to colleges and I recently got an email asking me to further elaborate on this identity. I was not planning on putting this as my race on the Common App, and I had forgotten that I had even put that as one of my races on my ACT until I received this email from a college. Should I contact the colleges I sent my ACT to about this? Or should I be fine as long as I do not mark it as my race on the Common App and I just explain my situation to the school in the future if they question why it says that on my ACT?
I think that you have stepped in the Elizabeth Warren pile. I definitely would NOT check the box on your common app, I would correct this now on your ACT profile, and I would send a letter to the colleges IF THEY ASK, stating the fact that your great grandfather was a Native American, but that you identify as White, do not have tribal citizenship, and that you only checked this on the ACT in an attempt to express your full heritage.
You can tell the college truthfully that your great-grandparent was American Indian, but you do not have tribal documentation. The college can do whatever it wants with that information.
Having a known* American Indian ancestor but not tribal documentation is probably somewhat common. However, many colleges do not treat that as anything special.
*Not really the same as the Elizabeth Warren situation, since her claim of such was based more on family legend of an ancestor further back, rather than one recent enough in generational terms to be known.