TTL for time-series collections is disabled when time-series collections contain data prior to 1970-01-01T00:00:00Z or after 2038-01-19T03:14:07Z.

Dates after 2038-01-19T03:14:07Z are sorted at the beginning of the clustered _id index and are not eligible for deletion.

However, if the collection only contains no data after 2038-01-19T03:14:07Z we could delete eligible data from the beginning of the _id index as long as we make sure it is eligible by inspecting the control field.

Data prior to 1970-01-01T00:00:00Z would still not get deleted but it would allow TTL to make progress on non-extended range data.