2) Should it be possible to have coins received in a wallet to an address that isn't shown in the address book (specifically when the address in question definitely had BTC sent from the outside as opposed to BTC left over from a sending transaction)
Yes absolutely, there are hidden keys in wallets, 100 by default
If you want to them all, use pywallet (sig)
I knew that there were 100 addresses pre-generated. What I meant was should they not show up in the address book once there are receipts against them. I don't know of a way to add them manually if they don't show up automatically. I do know that the walet .dat file can be moved to a new computer and the address book will be intact. I also know that I have another address with no description that doesn't disappear when it isn't the default like this one did.
Incidentally, I didn't get a new address in the "Your Bitcoin Address" section of the client after my last receipt (I should have mentioned this already, but I just now realized it, prior to that I was operating on the assumption that I might not have noticed the new address on my many previous receipts).