The author appears to have got a little confused about his
Scheiner degrees. This is not surprising because it is
a really confusing subject. He says that both Agfa Superpan
and Kodak SS were 23 degrees Scheiner.  Eastman SS Panchro
was 23 degrees American Scheiner which is more or less
the same as Weston 20 or ISO 50/18º.  This and one of
the other sites you listed does confirm that it was the
Agfa counterpart to Eastman Super Speed Panchromatic.

Scheiner degrees are based on the minimum exposure
required to give a visible deposit on the negative.
Julius Scheiner was particularly interested in
astrophotography and such a detection threshold system
probably made a lot of sense in that field, but it
is not particularly suitable for pictoral photography.
On top of this, the constants used in the American
and European versions of the formula are different,
and the European manufacturers tended to get more
optimistic as time went by - a phenomenon known
as "Scheiner inflation."

American Scheiner speeds tend to be about five degrees
higher than the corresponding DIN numbers, and
European Scheiner speeds tend to be about ten degrees
higher than the DIN speeds.  This is only a rough
approximation.  It is generally safe to assume that
a 30º Scheiner film made by a particular manufacturer
was about twice as fast as their 27º film, but there is
no guarantee that one manufacturer's 30º film was
any faster than another's 27º film.

Some of the other speed systems should be a more
reliable guide to how fast the old films were.

Assuming a fairly normal H&D curve shape:
ISO 50/18º corresponds to:
20 Weston
25 Old ASA
100 Kodak Speed (Jones)
1000 Ilford H&D

These are not based on the equivalence tables often
shown in books, but on comparing the ratings for the
same films in two or more different systems.
Kodak Speeds and Old ASA are different numbers
given for the same system. All of these numbers seem to
track each other very well in practice. If the shape
of the film curve is unusual, the relationships between
ISO, old ASA, Weston and Ilford H&D cannot be expected
to hold, but in the majority of films the relationships
hold very well.

Old DIN (1936-55) did not track particularly well
with the other systems. New DIN is the same as the second
number in the current ISO system. GE speed numbers were
usually 25% higher than old ASA ratings, but there
appear to be more exceptions to this than the rather
strong relationship between Weston and ASA speeds.

While H&D numbers were originally based on Hurter
and Driffield's work in 1891, and thus ought to
have been pretty much standardised, the ratings given
by different manufacturers in practice are not
necessarily comparable. For Ilford films and plates of the
1930s and 1940s Weston 20 equals 1000 H&D, but this
rule may not apply to other manufacturers' H&D numbers.

I'm not an expert on this, but I do have a bunch of
old books.

Peter.