Obviously it makes sense to reuse tapes after a reasonable amount of time has passed, EXCEPT when a case goes to trial.
Then the S.O.P. should surely be to preserve those tapes until it is certain they will no longer be needed. They are EVIDENCE, and it is KNOWN that they are evidence.
What does a tape cost, a couple of bucks? I think the department budget could afford it.
Why are they using tape at all? It should be fairly easy to come up with a system that records everything digitally, and then compresses the recording to some relatively low bitrate MP3 file once a call is over. You might be able to store many man-days worth of calls on a single DVD disc. (BTW, I used to use a lot of open-reel tape, and still have many open-reel recordings, but I haven't recorded anything to tape in four years or more.)
ML/NJ