Backfill to roll-over hdb3 files

I'm trying to backfill a year's worth of data for about 30k tags across two datasets using the gRPC write API extension methods. I'd like to backfill these into two new backfill datasets with daily hdb3 files. I figured out how to create daily files for the first tag using session.CreateNewFileAsync for the first day and then session.RollOverFileAsync after batching each day's worth of data. It took a while to figure out that the daily API roll-over will only work after disabling automatic roll-over in the Historian->Dataset config. When importing additional tags they all write to the latest dataset file no matter what I've tried.

Is it possible to backfill into old hdb3 files?