No individual needs to know all of it. But any team owning a system that reads data should know what they're using it for. Likewise anyone providing data to other teams should at least know which other systems are reading that data; even if they don't know for certain what the data is used for they know who to ask about it. So the process of understanding can easily be sharded, and the results merged in a fairly mechanical manner.

The timeline here seems to be that they were asked for this in December and required to produce it in January. It probably is unreasonable to get this done from scratch in that time. But if they haven't started a project to do it by now, then it does feel a bit like they prefer being able to say "we don't know".