cassettes
It CAN be done! Start loading some other file that does have a header. Then
simply stop the tape, and wind back/forward to the file with the lost header.
Start the tape again. The computer won't know you've moved the tape; it'll
think you're still loading the file you started with. Can't guarantee you'll
get all of the file with the lost header, but you should be able to recover
most of it. You'll have to edit the result: it'll contain part of the first
file you started to load, running without break into the file you've recovered.
You can even change tapes when you do this. Hint: after many cassette failures
I began planning for them. Expensive though it is, I now put only one file on
each tape–and I save it three times, just in case the "save" fails, or
something happens to part of the tape later.