So it’s lucky that when the company I worked for after working for Nixdorf went out of business, I spent my final minutes there on-site (we really didn’t get much notice to vacate the building),backing up my 8870 development system, and I kept the tape.
The problem is that these 9 track half-inch tapes don’t age well if they are stored in less than ideal conditions. The tape is actually made from a plastic material with a magnetic coating bonded to it’s surface using a hygroscopic glue (absorbs moisture from the atmosphere). What all this means is that if you start running an old tape through a tape drive there’s a good chance that the tape is going to fall apart and be ruined.
Lucky for me during one of my scouring the Internet for information sorties, I found VAXMAN. Go check out his site. We started Emailing as you do, and I happened to mention my problem with the tape, though I was more worried that I didn’t have an actual tape drive to read it on. VAXMAN offered to recondition the tape (by placing it a nice warm oven for a while which apparently doesn’t damage the magnetic coating or the data), and the reading it’s contents onto one of his VAX machines. He could then spool the data into a tape image that I could then read.
I got an Email from VAXMAN the other day saying the tape had arrived, but it may not be good news. Whilst the tape is physically intact there appeared to be a lot of parity errors when the tape was read, but hopefully, theres a good reason for this.

Another problem may be the “mode” that was used to write the tape. The 8870 supports two modes of operation; streaming and start-stop mode.