@Imp
Sure but most sources indicate that they were developed one after another, each time improved because the former needed to be improved.
@Cross
Well the infos on those 2 pages doesn't seem to match unfortunately.
The German source speaks of 90mm pentration for "PD 8,8cm-Pz.Büchsenrohr" & "Panzerblitz I" while the English one states 160-200mm, also that only the rocket motor was changed for the "Panzerblitz I" despite the German source indicating a much lower penetration value.
That the Panzerblitz I was called Panzerschreck 2 is also new to me.
As I said the infos about those systems are rare and most pages repeat what is found on others, that makes getting a definitive picture problematic at best.
Maybe someone stumbles about something definitive like a manual for those systems.
Here an example of manuals for the real Panzerschreck:
http://www.bergflak.com/psmanual.html