DSL has always been a derivative of Knoppix. In 2008, one of the DSL community members, Robert Shingledecker, had a falling out with the others and started Tiny Core Linux, which expanded support across hardware architectures to ARM and run on raspberry pi systems in addition to X86 / X86-64. TCL has been in development consistently since the 2008 split. DSL fell to the wayside from 2008 until seeing it get picked up this year.
Knoppix has abandoned the CDROM scale and is exclusively a DVD img release now. With the availability of USB flash drives, this makes a lot of sense. The live distro can boot from its static files, but utilize a writeable home directory on a separate partition on the flash drive thereby maintaining data across restarts.