Actually I think I know what is happening - you’re getting confused between imp001 cards (which have a mac address) and imp devices (which have an ID starting with “23” generally).
The imp card you originally said had a problem, 0c2a690047bb, has not connected since 12/22 at 10:17 UTC like I said 3 days ago. This was last seen in device 23370bb030728cee, but 10 mins before was seen in device 2341b84cead3dbee.
With the imp001, it is NOT the card that appears in the IDE. It is the device the imp is plugged into which appears in the IDE. Whatever device the imp is plugged into, it will run the appropriate code for that device - in effect you can swap imp cards that are blinked up to the same account around and nothing changes in the IDE - no new devices will appear. The server sees the card has changed, but it’s still on the same account and in the same device, so it carries on silently operating as it did before, with the same agent ID and everything.
I can see this:
0c2a690047bb was in 2341b84cead3dbee on 12/22 at 10:17 UTC
0c2a69001cd2 was in 2341b84cead3dbee 20 mins later
You then blinked up 1cd2 in 2341b84cead3dbee at 2017-12-23 21:40:16 on a new account.
When you moved it to a new account, you would see a new device appear because there’s no code associated with 2341b84cead3dbee in that account.