How to use brin_summarize_range

Good afternoon!

I am finding it difficult to understand how to maintain my BRIN index from
the docs. Specifically, this is the documentation on the
function brin_summarize_range which isn't clear to me:

brin_summarize_range(index regclass, blockNumber bigint) integer

- summarize the page range covering the given block, if not already
summarized

There is no information on how a user is to actually find blockNumber,
especially what blockNumber she might be interested in (like the end of the
table). On my table, my BRIN index is all of a sudden all out of whack and
I'm trying to figure out why. The planner doesn't choose it. Even if I
force a BRIN scan, it estimates way wrong, and performs terribly. I do not
have autosummarize on. I am curious if vacuum somehow invalidated
everything?

When I ran brin_summarize_new_values, it immediately returned 0. This
table has 292 million rows, and a straightforward insert-only pattern, but
we also prune data older than 1 year old. The BRIN index is on insert
time. It was working great up until just a bit ago.

Any direction on using these brin functions would be very appreciated.

Thanks,
Jeremy