I think I may have discovered the difference between the members who are showing "upgraded to other" and the members who had two active subscriptions at the same time.
The members who have the correct "upgraded to other" show the expiry date as the date they upgraded (I am assuming). The two members who have two active memberships at the same time must have done their upgrades after their current plan had expired. Their old subscription is still showing as December 31, 2015.
I have all of the plans only doing calendar years with 3 months grace period.
1.) Is the expiry date supposed to change to the date they upgraded for the old subscriptions?
2.) Are you allowed to upgrade after the expiry date? Possibly this is why it is screwing up.