My understanding of the Pali canon is that it is fairly fixed in form. That's to say, although there may be variations between Sri Lankan, Burmese, Thai etc. versions, probably due to various scribal errors down the centuries, we do not find differences of the sort you mention, such as suttas found in one version and not in another. The reason for this is simple. The Pali canon was pretty much fixed in the 5th c. CE by the commentators, and the various versions I mention are all later, but they all relate back to the the canon as the commentators describe it. So there is no scope for the kind of differences you are thinking might be found. What Brian was referring to is differences between the Pali version of texts like the Mahaaparinibbaana Sutta and other versions in Sanskrit, Chinese, etc.