I did use a referral, so I did receive 1,000 miles worth. Subsequently I became a referrer for one party we had delivery in Sep 2021. I added another 1,000 to my balance. The last of the resulting miles were to expire Mar 20, 2022 (70 of those left as of beginning of Feb).
I became another referrer around that same Sep, when the program still existed. That order was delivered a week or two ago, and again I received an additional 1,000 miles. I had 70 left set to expire in March. Right now my balance shows 1,070 expiring Sep 20, 2022. So interestingly enough the left-over miles about to expire seem to have been given an additional 7 months!