In order to limit the amount of data that is kept in the forward recovery and log of logs log streams, you might want to consider creating CICS® VR log stream copies of the forward recovery log streams.
Then, you can set a retention period for MVS™ blocks that is smaller than the retention period setting for log stream copies.
By setting an MVS blocks retention period that is smaller than the log stream copies retention period, you can limit the amount of data retained in the MVS log streams without losing the ability to recover VSAM spheres from updates made over the required amount of days. However, be sure you are creating and keeping backups according to your recovery requirements.