I've only deactivated Facebook, not deleted. I'm worried that if I completely delete I have no way left to access the data Facebook has on me. Is anyone aware of how their shadow profiles work? If I deactivate, are they still able to attribute things like someone uploading my number from their contacts back to my profile?

It's this reason that I haven't nuked it entirely yet. I also use Messenger on occasion to communicate with those I haven't spoken to in a long time. I'm ready to make that leap soon. And no, not all of those folks whose numbers or email addresses I lack are not 'friends' necessarily - I have a few former colleagues and bosses on there as well I like to chat with on occasion.