Re: IndexUpgrader not upgrading indices?

> I have indices that were written with Lucene 9.x and upgraded using
> IndexUpgrader to 10.x (along with the code that uses them). When
> attempting to add new data to the upgraded indices (using the
> IndexWriter.addIndexes method), I'm getting this exception:

So I found <https://github.com/apache/lucene/issues/9311>, and it
looks like Lucene major upgrades are expected to be followed by full
re-indexing? The IndexUpgrader allows searching on old indices, but
isn't a tool for really upgrading indices to be fully used by new
Lucene releases? That's from 2018, but I'm not finding anything newer
to contradict it. Updates would be very welcome though.