Yeah, I realised I got the probability wrong but haven't written a follow up (typing on my phone is tough, writing code is impossible). The probability of being

Yeah, I realised I got the probability wrong but haven't written a follow up (typing on my phone is tough, writing code is impossible). The probability of being able to update an old version of the document, is simply 1/ 65536. That's a very high probability given thousands of documents or a modest number of competing updates. The biggest issue is that it's undetectable and non-deterministic: the update that should fail will succeed silently and it can happen at any time. I'll re-open the bug in the morning with a proof-of-concept.