There is also a DLT-specific FAQ maintained by Larry Kaplan from Quantum. Likewise the 20 GB cartridge is 10 GB native. Double the capacity. Some agreement with Cypher. You're comparing the top QIC format with the rather new DLT tecnology.
Serpentine format means that there are several parallel tracks.
So it looked like a 54 track cartridge. ANSI standard, but that does not mean anyone other that DEC is doing anything more than OEM'ing it.