Actually, if memory serves me, they only book the impairment IF they have stock transactions and "realize" the price change. I don't know if F and AMZN sold any shares in Q1, but if they did not, they don't have to book the impairment.
If I'm wrong, please correct me and point to relevant guidelines.
I don’t know if you’re wrong, but they definitely booked unrealized gains last quarter - it doesn’t make sense that they wouldn’t have to show the loss on the way back down.