How loose is the "date of system action."  I ask because on a book I mailed, it had been expected date of delivery 3-10-2011, date of system action 3-11-2011.  But today it appears to have declared it lost within my transaction archive?

It isn't unexpected either way (I have already contacted the receiver to make sure it wasn't delivered and had been planning on filling out the "Mail Theft" form from USPS.  (It is kind of sad the book was in great condition and is Wishlisted, they are the WL'er behind me so now I have to hope that someone else adds one to the system).

I was just thrown when it had already moved it today, and began to wonder what the sequence of system actions are?

I've noticed this too. If you add it up, it times out on 26 days. For some reason they give the date of system action at 28 days though. I've never really understood, but it happened to me twice when a couple books went lost.

Yes, it says the system action date is in..28 days.. when it is actually 26 days to when the book will go lost. There's no real reason for it other than they don't want people to contact them for 28 days so that's how its written. I've asked about it and they know its inconsistent, but not a real high priority in their to-do list.

OK, given the post offices record it shouldn't be a high priority anyways so that makes sense.

Follow Up Question:

Filling out the Mail Theft form, I didn't record the requestor's address except on the package.  I don't seem to find the address in my transaction archive.  Is it available short of asking the requestor for it again?

No, you'll have to PM the recipient and ask them to provide that information again.