Question: Can changes be presented multiple times or missed?

From the documentation, I was unable to discern the answer to the following question - I hope I'm wrong, but I feel I've spent reasonable time trying to answer the question myself. Asking here as it might form a good documentation request and/or a place to put a canonical answer...

As one scales up and down to multiple partitions, what are the guarantees provided by the ChangeFeedProcessor as a whole wrt the following:
- not missing documents - i.e., can I trust that a split or merge will _never_ result in me missing an insert.update ?
- not seeing documents multiple times except when a checkpoint write is lost - i.e. if one was to checkpoint after every write, would you ever see the same documents presented to the observer callback multiple times as a result of the merge or split ?

(I'm thinking reading the integration tests and/or source will give me hints, and I'll do some testing, but it would really help me _a lot_ if someone would be so kind as to give me an answer in advance of me doing the legwork!)