recycling tapes

You can't recycle tapes until all the images have expired.  Short of copying the non expired images to new media you will have to wait.

You need sufficient cartridges to hold the images + new until old tapes expire, which, providing you do not allow mixed retention periods on a media, will be 1 year after the last image is written (if the retention period of all the images on the tape is 1 year)

Allowing mixed retention periods is possible, but no recommended.  You may for example have a tape full of 1 month retention images, but also a single 1 year retention backup which should really have gone on a 1 years retention period only tape.  In other words, mixed retention periods use more tapes.

Disk does not have this issue - however a report I read stated on average, more data is lost to disk failure than tape ... worth bearing in mind ...