If drivers have already implemented DRIVERS-464, they need to update their implementation of how they initially store startAtOperationTime. Instead of setting a default startAtOperationTime when the ChangeStream is created, drivers must omit a default startAtOperationTime. When resuming, drivers must use the operationTime of the initial aggregate command as the default startAtOperationTime value.

See https://github.com/mongodb/specifications/commit/745debcf4624ec820eb9b138cd8f28fa7b1e5782 for the exact implementation details.