At $50+ per cartridge, they better be reliable.  I do not know the
documented claims of lifespan or read & write passes, but have used the
following technique.

As long as you don't have any write errors, I would continue using them.
ADSM will stop writing to a tape when it gets a write error & mark the tape
as READOnly.  You can query all your volumes by issuing;
        "query volume access=readonly format=detailed"
If this command lists any tapes, look for "Number of Write Errors" and
especially "Number of Read Errors" with counts over zero.  (A tape with a
read error may be marked as UNAVailable, I am not sure.  I've never had one)

I moved into a new shop with ADSM running with 3490 tapes & found 6 tapes,
each with a write error.  I took note of the volume labels, migrated the
data off them & allowed them to be re-used.  After they had filled up,
checked them again for any errors & retired any with any errors.