An open source implementation of SCCS, found via https://minnie.tuhs.org/pipermail/tuhs/2022-June/025898.html
The comparison to RCS on http://sccs.sourceforge.net/sccs_vs_rcs.html appears to be one-sided, but then I am probably biased towards RCS, which was the first version control software I have used.
http://sccs.sourceforge.net/sccs_invention.html sounds like an interesting read.
The last message on the mailing list https://sourceforge.net/p/sccs/mailman/sccs-devel/?viewmonth=201510 I found had been written 2015-10.
According to https://de.wikipedia.org/wiki/J%C3%B6rg_Schilling, the author Jörg Schilling passed away on 2021-10-10.
TODO: find out the license