Originally Posted by reft

This typically refers to miles earned, but not yet transferred to your FF account. it does not generally refer to miles already in your FF balance. You would have to do something egregious to get a 'clawback'



Yes. Activity can come from the CC, flights, points purchase or redemption. Since AA and US are merging, likely you want to keep an an eye out for any rules changes over the next 24 months as things settle out.

If you don't have activity for 18 months, don't wait until the last minute to generate it. Give yourself at least a month.