Of course, some of them are probably still mothballed because of the pandemic. The demand is only growing, so obviously they are not all being put back into service at the same time. That is a gradual process, which is ongoing.
With respect to your question—it's a very good one—one of the required actions to be taken before the return to service of any particular aircraft is to follow a Boeing service bulletin—which was developed specifically to address your question—to consider the specific maintenance actions that should be undertaken on an aircraft that has been stored for such a period of time. I believe those back-to-service maintenance actions are customized, dependent upon where and how the aircraft was stored. It was definitely part of the process to make sure that was covered.