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Question regarding ISO 532 B and DIN 45 631

I have been looking at these two standards.  I have three programs which
calculate loudness;  one, I wrote in matlab based on a BASIC program
submitted to Acustica, Vol. 55 (1984), one, a matlab program another member
of the group was kind enough to send me, and one I found on the internet.
Both matlab programs plot the specific loudness as well as giving total
loudness.  My problem is this, there is an example on the second to last
page of DIN 45 631 which deals with a 1000 Hz pure tone with a level of 70
dB.  In the DIN standard, it gives a total loudness of 8.02 sones.  The
shape of the contour is three stair steps (from left to right) then a smooth
slope.  All three programs that I have tried for this have given a level of
7.4 sones (for free field).  Further, the two matlab programs have only one
stair step and then a slope.  It seems like all three programs are not
getting the accessory excitation for the lower frequencies correct.  As far
as I know all three programs were written independently although they may
all (mine at least is) be based on the Acustica, Vol. 55 (1984) article.

Question:  Does anyone know if there was something wrong with the Acustica,
Vol. 55 (1984) program?
Question:  Does anyone have any comments /  suggestions?