If you look at the data that the MyDrive smartphone app shows for each device, you'll notice that the "lifetime subscription" has a fixed expiry date. It appear

If you look at the data that the MyDrive smartphone app shows for each device, you'll notice that the "lifetime subscription" has a fixed expiry date. It appeared to be ~10 years for the devices I looked at. I could not see this information any other way except via the MyDrive app.