I believe your understanding is correct. Checks that were placed in the mailbox or handed to the recipient are recorded as of the date they were handed over, not the date the payee deposited them. Checks that were still in your possession are not recorded until they are handed over or placed in the mail.
Note that you must have funds in the bank account to clear the check. If you handed over a check on Sept 29 and you had insufficient funds, and told the payee to hold onto the check until October 2 so you could deposit funds, then the "funds" have not left your control until October. Likewise, if you mailed the check on September 29, but it was post-dated to October, then it is recorded in October.
