I read social media last evening that confirms your theory. It does take 1 or 2 days for the organ donation process to be completed. (We have seen this in a couple of instances in the last year or so....)
I am more familiar with Lakota beliefs and organ donations. The belief held by many Lakota members is a part of the body should not be left on the Earth after death; they are not very open to organ donations, although this is very, very slowly changing.
NA belong to a separate country. They have dual national NA/tribal and US citizenship and have control over their own affairs. As to the lack of information, my guess is the tribe is not giving this out. Perhaps you recall the Red Lake (MN) school shootings. Tribal members there were overwhelmed by the media attention and uncomfortable with outsiders offering help.