When to recycle logical log back up tapes

Hi, We have Informix OnLine 7.22 running on Windows NT 4.0. We are making daily full system backups , our database is small , about 10000 records in the main tables ( although using Byte blobs and Text blobs). We are also continously backing up the logical logs. Whenever my full system data backup finishes successfully, the next logical log to be backed up is appended to the end of the logical log tape ( no matter if before starting my full system data backup I stop the continous logical log backup and I restart it whenever the data backup has finished). That means that there is a moment when the logical log backup tape gets full, and the engine asks me to insert another tape in the corresponding drive. My question is : When do I know I can recycle one of the logical log tapes. Wouldn't it make more sense that whenever a full system data backup is finished successfully the Informix engine would know how to rewind the corresponding logical log tape and start overwriting the old logical logs? Or at least give you that option? What do I need logical logs previous to my last full system data backup for? For the backup procedure we are using the user interface provided by Informix 7.22 that indirectly uses ONBAR ( instead of ontape). Thanks. Susana.