Originally Posted by
antonius66
So to be clear, if I move from Iberia to BA it will show the expiration date for those same miles that they had when in the Iberia account, when they show up in the BA account and I could theoretically then move them back to Iberia? Basically that would just be a way to have them in the BA account because the BA account displays the expiration date and the IB does not?
No. The BA expiry date is the BA expiry date. And maybe you have had even less activity with BA, meaning that any transferred Avios would expire immediately. But in general BA's a safer place to hold Avios if you're the kind of person who only earns or burns Avios every 2-3 years. (because you can track the expiration date and many people find it easier to keep a BA account active)
For the avoidance of doubt, Avios expire 36 months after the last earning or burning activity. AFAIK everything counts as activity except "Combine my Avios" and possibly buying Avios.
If you're going to be holding 5 or 6 figure Avios balances with almost no activity, I recommend that you figure out a way to remain active. It's not that hard - online surveys, etc. are an easy and free way of earning a few Avios and remaining active.