timeseries::MinMax::minUpdates/maxUpdates returns updates that have been made to the min/max since the last time the function was called. However, really it should really also consider any calls to timeseries::MinMax::min/max.
The timeseries::MinMax usage pattern for time-series inserts is that timeseries::MinMax::min/max is called when a bucket is first created, and then subsequent inserts which update an existing bucket use timeseries::MinMax::minUpdates/maxUpdates. This means that, due to the behavior described above, the first call to timeseries::MinMax::minUpdates/maxUpdates for a given bucket includes updates for the entire min/max, as opposed to just the changes since the bucket was originally inserted. This is not a correctness issue, but does mean that applying the diff to the bucket may be doing extra unnecessary work in this case.