That's what I did.
I should've realized when you said you were successful with at least one tape.
I have a number of 4mm DATs from that era. I will have to purchase a DAT drive. And load those tapes. At least I know how now.
If you don't feel like buying one or can't find a suitable one, I'd be happy to dump the tapes to files for you. I have two SCSI DAT drives, one DDS-3 and one DDS.
Hope somebody appreciates the trouble I'm going through. 
It's appreciated! Thanks!