I agree with StepAway, if Everybody is supposed to do it, Nobody does.
I also have first hand knowledge of the way social services work (though not child protection, I am talking about one borough as well, but it's actually a well regarded one I've been told! ), and also how cross agency communication works. It is bad I'm afraid. I'm sorry if I get jumped on for 'ss bashing', but this is my experience.
Proper notes are not kept, or weren't in my experience. Continual errors were recorded as fact, as soon as something was written down, even when totally and probably wrong, the fact that 'it was in the notes' is used as evidence that it's true.
Assumptions, identity confusion, miscommunication and an over riding belief that there is no definitive 'facts' but just beliefs that are weighted to the influence of the person saying them. Senior staff who do not know their basic responsibilities or statutory obligations. Staff who make up anything to please their immediate line manager.
The huge amount of inaccuracies make any kind of truth seeking completely impossible, and that's with a case where the person was completely positively engaged and actively seeking correction of basic fundamental errors. In one single document I counted 56 errors (not typos or grammar, actual factual errors!). How can you possibly do a good job with that even if you wanted to?!
Meetings took place using these highly inaccurate sources of information. Decisions were made on them and no discussion was ever allowed and error upon error was used to justify their decisions, and no record could ever be found of the raising / correction of a key fact, even when this was resent again and again.
It's like a whole institution exists to make anyone who works there's life difficult, and any sense of professionalism is buried under a mountain of bad working practise, illogical processes, often failing to adhere to basic legislation set out by the government.
I'm afraid I can see exactly how these tragedies happen. The thing I don't get is why this doesn't happen more often. I believe that it's down to the massively over worked few that work right on the 'coal face' using their brains and doing good even when the entire system is weighted against them being able to do anything.