The Ninth Circuit holds that the "mailbox rule" applies to petitioners who seek relief from deportation and who are in detention at the time they file their appeal, and that the required declaration that states that the petitioner is indeed in detention and placed the appeal in the facility's outgoing mail system on X date may, but need not, be filed with the original papers, and instead may potentially be filed later.
The Ninth Circuit's opinion in this regard seems entirely right to me.
The Ninth Circuit cautions, however, "the court has discretion to reject or to give less
weight to a declaration or affidavit that does not accompany
the inmate’s legal filing." It does so on the basis of the reasoning of the Eighth Circuit that "[a]n
affidavit filed long after the events in question
have occurred tends to be less trustworthy
than a promptly-recorded statement because
the passage of time dulls memories."
That's true. To a degree. Memories about precisely what day it was when you did Y may indeed fade over time.
But there's another reason to credit early-filed declarations as well.
Sometimes, you only realize that a filing was due on Day X after the court, or your opposing party, files papers that say that your petition should be dismissed because it wasn't received until Day Y. It may potentially be only at that point that you realize that, crap, it was due on Day X. You at that point discover the mailbox rule, and -- now cognizant that your mailing needed to be on Day X -- submit a declaration that says, yep, that's exactly when I mailed it. You have a large incentive to so recall.
By contrast, if you originally submit a declaration that says you mailed it on Day X, that may not prove that you mailed it on that day. But it at least helps to establish that at the time you filed your petition, you likely knew at the time it was due on Day X, and that your declaration wasn't merely a response to someone belatedly telling you that it was due on that day. And if you knew it was due on Day X at the beginning, that's some evidence that you likely in fact filed it by that day.
So it's not just "faded memories" that an early filing may help with. It's also any alleged fabrication.
So a good rule here. For multiple reasons.