In case of Facebook ads, you can check advertisers whose ads you clicked on the same page where you check who uploaded your data.
In my case it shows... 2x more than I expected, but looking at the names, most of those were most likely pictures of t-shirts, or funny videos, that I just clicked to check out.
The GUI interface shows 0 activity across the board.
The data download is much more helpful and complete - shows two ad actions of "action": "closed ad" within the past 2 weeks, one of which I would have been asleep. It confirms they don't have my phone or any other alternate email, other than the @facebook.com address they auto-generate for everyone. I'm thinking now that maybe someone realized that Facebook did this and set out to grab usernames via the graph and added emails to their list that contained username@facebook.com. Best theory at the moment since that sounds exactly like something a growth hacker would come up with. The data download doesn't tell you which email address the advertisers provided from their list, which would settle this pretty quick.
In my case it shows... 2x more than I expected, but looking at the names, most of those were most likely pictures of t-shirts, or funny videos, that I just clicked to check out.