They have a representative sampling in the hundreds of thousands of readings. Sure, they're going to refine their estimate, and the purpose of the initial release is so that their peers can review their work... but it's dishonest to pretend that they either don't have access to data, or that the new total release estimate is new data that they lacked.
Well... dishonest or ignorant. Take your pick.
Funny you should talk about a deep cavern... because that is where the corium of the 3 leaking reactor "ex-containers" is going.... Down into the ground.
Which puts you firmly into chemtrail conspiracy fantasy land.
And where does this cavern sit? Why, right on the edge of the ocean. An ocean into which groundwater discharges.
And yet the ongoing monitoring of the sea right next to the reactors and for miles out fails to pick up this discharge?
Oh wait... I know. All of the universities/provinces/agencies involved are all in on the lie, right?
And what do people eat? Why, they eat fish that comes from the ocean that the corium is flowing into.
And the fish is also checked for contamination. That's all part of the conspiracy too, right?
Why can't you see this simple stuff? Even the report makes mention of these future impacts
Of course it does... because the dose is ongoing. But that doesn't mean that they can't estimate the dose received to date.
Just as importantly (and what you persist in ignoring), there are actual dose measurements that have been done (in one case they specifically mention, over 1,000 children in the area they expected the highest doses). The actual doses measured were significantly lower than the high end of the WHO/UNSCEAR estimates. Which clearly indicates that they've been conservative. So again, it's ignorant/dishonest to claim that they're lying in an attempt to allay fears.