If you want it on the same tape, you would specify "append" and the same media set as the nightly job.
But if you cycle your nightly tapes (every two week, say), then the Archive data would be overwritten also
If you have a loader, you would use a separate Media Set with a perm OPP and make the job either "overwrite" to put each archive on it's own tape, or "Append" to stack them on the same media