Again, there ARE definition changes.
From [1] (an article you referenced):
> When a person has more than one account and takes > actions (such as liking photos or adding comments) on the separate accounts, these actions may be counted separately even though they were made by the same person.
Notice the "may be counted" part (which is pretty vague and it's hard to argue the definition hasn't changed on a vague statement). Judging by the their latest announcement [2], by mentioning "may be counted" in [1], they probably meant this:
- If that persons' email was the same on two or more accounts, or they used the same mobile device, we'll count it as the one person
- Otherwise, we'll count it as a different person
Again, I'm quoting this part from [2]:
> For example, if someone used the same email address across their Facebook and Instagram accounts or accessed both platforms from the same device, we counted them as one person when they interacted with ads.
The definition of "may be counted" will essentially change after Facebook implements their counting update to:
- If a person didn't link their accounts under "Accounts Center", we'll count them as 2 people
- Otherwise we'll count them as one person
So Facebook won't make any attempts to implicitly associate 2 accounts as 1 person using emails/device IDs as they did in the past.
Based on the available data, the definition of what Facebook counts as a "unique person" HAS changed.
[1] https://www.facebook.com/business/help/283579896000936
[2] https://www.facebook.com/business/news/an-update-on-how-we-c...