@AeroMan:
There's an episode where there is a picture of one of Bender's ancestors on the wall, and the caption reads "COMMODORE LXIV". It's really quick. I didn't catch it right away. A few minutes later I was ROFLing.
@Spihunter:
If C= written tapes are as good as C= written disks, I'd guess your tape is still good. C= disk drives have very strong magnets. On an Apple ][, you could always use both sides of single sided disks. With C= drives, unless you had really good double sided disks, writing on one side would trash the other.
Besides, for some reason, tapes stay magnetised a long time as long as you don't store them on top of your monitor.