Possibly silly question, but I can't find an explicit answer for this in the aggregations docs.
From the docs:
The context of the execution defines what this document set is (e.g. a top-level aggregation executes within the context of the executed query/filters of the search request).
I am assuming this context is also defined by the max-result-window. And if there are aggregatable docs beyond that initial limit, they may not be counted. Hence it is possible for bucket aggregation to return 0, if the bucket conditions are not met within the first 10000 results?